U.S. patent application number 15/140036 was filed with the patent office on 2016-12-08 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 Akira KIMURA, Tsuyoshi NAKAJIMA, Hiroyuki ONO, Takanori TAGO, Hideo WATANABE.
Application Number | 20160354644 15/140036 |
Document ID | / |
Family ID | 57450780 |
Filed Date | 2016-12-08 |
United States Patent
Application |
20160354644 |
Kind Code |
A1 |
WATANABE; Hideo ; et
al. |
December 8, 2016 |
MULTI-PIECE SOLID GOLF BALL
Abstract
In a golf ball having a core, a cover and an intermediate layer
therebetween, the ball and a sphere consisting of the core encased
by the intermediate layer have surface hardnesses which satisfy a
specific relationship, the intermediate layer and the cover have
thicknesses which satisfy a specific relationship, and the core has
a hardness profile in which the hardnesses at the core center, at
positions 5 mm, 10 mm and 15 mm from the core center and at the
core surface satisfy specific relationships. This ball, when played
by mid- and high-level amateur golfers, achieves a good distance on
driver shots, has a soft feel at impact and maintains the spin
performance at a high level on approach shots.
Inventors: |
WATANABE; Hideo;
(Chichibushi, JP) ; KIMURA; Akira; (Chichibushi,
JP) ; NAKAJIMA; Tsuyoshi; (Chichibushi, JP) ;
TAGO; Takanori; (Chichibushi, JP) ; ONO;
Hiroyuki; (Chichibushi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bridgestone Sports Co., Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
Bridgestone Sports Co.,
Ltd.
Tokyo
JP
|
Family ID: |
57450780 |
Appl. No.: |
15/140036 |
Filed: |
April 27, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A63B 37/0031 20130101;
A63B 37/0092 20130101; A63B 37/0043 20130101; A63B 37/0063
20130101; A63B 37/0068 20130101; A63B 37/0077 20130101; C08K 5/14
20130101; C08L 9/00 20130101; C08K 3/10 20130101; A63B 37/0045
20130101; C08K 5/098 20130101; C08K 5/098 20130101; A63B 37/006
20130101; A63B 37/0033 20130101; C08L 9/00 20130101; A63B 37/0051
20130101; A63B 47/008 20130101; C08K 5/14 20130101; A63B 37/0039
20130101; A63B 37/0075 20130101 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 4, 2015 |
JP |
2015-113941 |
Claims
1. A multi-piece solid golf comprising a core, a cover and an
intermediate layer therebetween, wherein a sphere comprising the
core and the intermediate layer which peripherally encases the core
(intermediate layer-encased sphere) and the ball have respective
surface hardnesses, expressed in terms of Shore D hardness, which
satisfy the relationship: surface hardness of ball.ltoreq.surface
hardness of intermediate layer-encased sphere; the intermediate
layer and the cover have respective thicknesses which satisfy the
relationship: cover thickness.ltoreq.intermediate layer thickness;
and the core has a hardness profile which, expressed in terms of
JIS-C hardness, satisfies conditions (1) to (6) below, wherein Cc
is the JIS-C hardness at a center of the core, C5 is the JIS-C
hardness at a position 5 mm from the core center, C10 is the JIS-C
hardness at a position 10 mm from the core center, C15 is the JIS-C
hardness at a position 15 mm from the core center, and Cs is the
JIS-C hardness at a surface of the core: 20.ltoreq.Cs-Cc, (1)
0<C10-Cc.ltoreq.10, (2) C10-Cc<Cs-C10, (3) 15<Cs-C10, (4)
Cs.gtoreq.80, (5) and Cc.gtoreq.52. (6)
2. The golf ball of claim 1 which further satisfies condition (3')
below: (Cs-C10)/(C10-Cc).gtoreq.3. (3')
3. The golf ball of claim 1 which further satisfies condition (1')
below: 26.ltoreq.Cs-Cc. (1')
4. The golf ball of claim 1 which further satisfies condition (7)
below: (C10-C5).ltoreq.(C5-C0).ltoreq.(Cs-C15).ltoreq.(C15-C10).
(7)
5. The golf ball of claim 1, wherein the core is formed of a
material molded under heat from a rubber composition comprising:
(A) a base rubber, (B) an organic peroxide, and (C) water or a
metal monocarboxylate or both.
6. The golf ball of claim 1 wherein, letting tan .delta..sub.1 be
the loss tangent at a dynamic strain of 1% and tan .delta..sub.10
the loss tangent at a dynamic strain of 10% when the loss tangents
of the core center and the core surface are measured at a
temperature of -12.degree. C. and a frequency of 15 Hz, and
defining the tan .delta. slope as (tan .delta..sub.10-tan
.delta..sub.1)/(10%-1%), the difference between the tan .delta.
slope at the core surface and the tan .delta. slope at the core
center is larger than 0.002.
7. The golf ball of claim 1 which satisfies the condition
V.sub.0-V.sub.60<0.7, where V.sub.0 is the initial velocity of
the core in the golf ball after the intermediate layer and cover,
collectively referred to as "the core-covering layers," have been
molded, as measured after peeling away the core-covering layers,
and V.sub.60 the core initial velocity measured 60 days after
measuring V.sub.0.
8. The golf ball of claim 1, wherein the intermediate layer is
formed of a resin composition comprising: a combined amount of 100
parts by weight of the following two base resins (I) and (II): (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 (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
% blended in a weight ratio (I):(II) of from 90:10 to 10:90; (III)
from 1.0 to 2.5 parts by weight of a basic inorganic metal compound
capable of neutralizing un-neutralized acid groups in the resin
composition; and (IV) from 1 to 100 parts by weight of an anionic
surfactant having a molecular weight of from 140 to 1500, and
wherein the component (I) and (II) resins each have a melt flow
rate of 0.5 to 20 g/10 min, component (I) and component (II) have a
melt flow rate difference therebetween of not more than 15 g/10
min, the composition comprising components (I) to (IV) has a melt
flow rate of at least 1.0 g/10 min, and a molded material obtained
by molding the composition under applied heat has a Shore D
hardness of 35 to 60.
9. The golf ball of claim 1 wherein, when the core surface is
photographed with a camera and image data collected by the camera
is image processed in such manner as to identify and digitize
scratches appearing on the core surface, the number of digitized
scratches is 100 or more.
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. 2015-113941 filed in
Japan on Jun. 4, 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 of three or more pieces having a core, an intermediate layer
and a cover.
BACKGROUND ART
[0003] In the art relating to golf balls of two or more pieces
having a core and a cover and multi-piece solid golf balls of three
or more pieces having a core, an intermediate layer and a cover, a
number of disclosures have hitherto been made which focus on the
hardness profile in the core or on the hardness relationship
between the intermediate layer and the cover, the intermediate
layer material and the like. Such golf balls are described in, for
example, US 2014-0187351 A1, JP-A 2011-120898, JP-A 2010-214105,
JP-A 2010-172702, JP-A 2008-194474 and JP-A 2008-194473.
[0004] However, there is room for further improvement in the core
hardness profile of such golf balls. In particular, there exists a
desire to provide golf balls which, by optimizing the core hardness
profile and the overall hardness and thickness parameters of the
ball, are able to achieve the intended spin properties and thus an
increased distance. Moreover, in these golf balls, there is a
desire not only for increased distance, but also, to increase the
enjoyability of the game, for the ability to maintain the spin
performance on approach shots at a high level.
SUMMARY OF THE INVENTION
[0005] It is therefore an object of this invention to provide a
multi-piece solid golf ball which retains a good distance on shots
with a driver (W#1) yet has a soft feel at impact and which,
moreover, is able to maintain the spin performance on approach
shots at a high level.
[0006] As a result of extensive investigations, we have discovered
that, in a multi-piece solid golf ball having a core, a cover and
an intermediate layer therebetween, by adjusting the design of the
core hardness profile and hardness gradient such that the hardness
gradient out to a position 10 mm from the core center is not very
steep but the hardness gradient further out from the core interior
is steeper, with the hardness difference between a position 10 mm
from the core center and the core surface, expressed in terms of
JIS-C hardness, being greater than 15, and moreover by constructing
the ball such that the intermediate layer is thicker than the cover
and the surface hardness of an intermediate layer-encased sphere is
higher than the surface hardness of the ball, the spin rate on full
shots with a driver (W#1) can be held lower than in conventional
golf balls, enabling an increased distance to be achieved, in
addition to which a soft feel at impact can be obtained.
[0007] Hence, we have succeeded in developing a superior golf ball
which, particularly for the mid- or high-level amateur golfer whose
head speed is not as high as that of a professional, retains the
spin performance on approach shots at a high level while
maintaining a good distance on shots with a driver (W#1), and thus
provides good enjoyability in the game of golf. In addition, the
golf ball of the invention also has an excellent resistance to
damage of the cover surface (scuff resistance) when struck with a
fully grooved wedge. As used herein, "mid- and high-level amateur"
refers to golfers having head speeds (HS) of generally 40 to 50
m/s, with a mid-level amateur golfer having a HS of about 40 to 48
m/s and a high-level amateur golfer having a HS of about 42 to 50
m/s.
[0008] Accordingly, the invention provides a multi-piece solid golf
having a core, a cover and an intermediate layer therebetween,
wherein a sphere made up of the core and the intermediate layer
which peripherally encases the core (intermediate layer-encased
sphere) and the ball have respective surface hardnesses, expressed
in terms of Shore D hardness, which satisfy the relationship:
[0009] ball surface hardness.ltoreq.surface hardness of
intermediate layer-encased sphere; the intermediate layer and the
cover have respective thicknesses which satisfy the relationship:
[0010] cover thickness.ltoreq.intermediate layer thickness; and the
core has a hardness profile which, expressed in terms of JIS-C
hardness, satisfies conditions (1) to (6) below, wherein Cc is the
JIS-C hardness at a center of the core, C5 is the JIS-C hardness at
a position 5 mm from the core center, C10 is the JIS-C hardness at
a position 10 mm from the core center, C15 is the JIS-C hardness at
a position 15 mm from the core center, and Cs is the JIS-C hardness
at a surface of the core:
[0010] 20.ltoreq.Cs-Cc, (1)
0<C10-Cc.ltoreq.10, (2)
C10-Cc<Cs-C10, (3)
15<Cs-C10, (4)
Cs.gtoreq.80, (5)
and
Cc.gtoreq.52. (6)
[0011] In a preferred embodiment, the golf ball further satisfies
condition (3') below:
(Cs-C10)/(C10-Cc).gtoreq.3. (3')
[0012] In another preferred embodiment, the golf ball further
satisfies condition (1') below:
26.ltoreq.Cs-Cc. (1')
[0013] In yet another preferred embodiment, the golf ball further
satisfies condition (7) below:
(C10-C5).ltoreq.(C5-C0).ltoreq.(Cs-C15).ltoreq.(C15-C10). (7)
[0014] The core of the golf ball is preferably formed of a material
molded under heat from a rubber composition containing: (A) a base
rubber, (B) an organic peroxide, and (C) water and/or a metal
monocarboxylate.
[0015] In the golf ball of the invention, letting tan .delta..sub.1
be the loss tangent at a dynamic strain of 1% and tan
.delta..sub.10 be the loss tangent at a dynamic strain of 10% when
the loss tangents of the core center and the core surface are
measured at a temperature of -12.degree. C. and a frequency of 15
Hz, and defining the tan .delta. slope as (tan .delta..sub.10-tan
.delta..sub.1)/(10%-1%), the difference between the tan .delta.
slope at the core surface and the tan .delta. slope at the core
center is preferably larger than 0.002.
[0016] The golf ball of the invention preferably satisfies the
condition V.sub.0-V.sub.60<0.7, where V.sub.0 is the initial
velocity of the core in the golf ball after the intermediate layer
and cover, collectively referred to herein as "the core-covering
layers," have been molded, as measured after peeling away the
core-covering layers, and V.sub.60 is the core initial velocity
measured 60 days after measuring V.sub.0.
[0017] In the inventive golf ball, the intermediate layer is
preferably formed of a resin composition containing: a combined
amount of 100 parts by weight of the following two base resins (I)
and (II): [0018] (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 [0019] (II) an
olefin-acrylic acid binary 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
% blended in a weight ratio (I):(II) of from 90:10 to 10:90; [0020]
(III) from 1.0 to 2.5 parts by weight of a basic inorganic metal
compound capable of neutralizing un-neutralized acid groups in the
resin composition; and [0021] (IV) from 1 to 100 parts by weight of
an anionic surfactant having a molecular weight of from 140 to
1500. In this embodiment, the component (I) and (II) resins each
have a melt flow rate of 0.5 to 20 g/10 min, component (I) and
component (II) have a melt flow rate difference therebetween of not
more than 15 g/10 min, the composition of (I) to (IV) has a melt
flow rate of at least 1.0 g/10 min, and a molded material obtained
by molding the composition under applied heat has a Shore D
hardness of 35 to 60.
[0022] In a further embodiment, when the core surface is
photographed with a camera and image data collected by the camera
is image processed in such manner as to identify and digitize
scratches appearing on the core surface, the number of digitized
scratches is 100 or more.
Advantageous Effects of the Invention
[0023] The multi-piece solid golf ball of the invention, when
played by mid- and high-level amateur golfers, achieves a good
distance on shots with a driver (W#1), has a soft feel at impact
and maintains the spin performance at a high level on approach
shots, providing good enjoyability in the game of golf. In
addition, this golf ball has an excellent resistance to damage of
the cover surface (scuff resistance) when struck with a fully
grooved wedge.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0024] FIG. 1 is a schematic sectional diagram of a golf ball
according to an embodiment of the invention.
[0025] FIG. 2 is a diagram illustrating a method of obtaining a
test specimen for measuring the bond strength between the core and
the intermediate layer of a golf ball.
[0026] FIG. 3 is a schematic diagram showing the apparatus used in
the examples to photograph a portion of the core surface.
[0027] FIG. 4 is an image showing a portion of a core surface that
has been photographed by the apparatus in FIG. 3 and
image-processed.
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 foregoing diagrams.
[0029] The multi-piece solid golf ball of the invention has, in
order from the inside: a solid core, an intermediate layer, and a
cover. Referring to FIG. 1, which shows the internal structure of
one embodiment of the inventive golf ball, the golf ball G has a
core 1, an intermediate layer 2 encasing the core 1, and a cover 3
encasing the intermediate layer 2. Numerous dimples D are typically
formed on the surface of the cover 3 to improve the aerodynamic
properties of the ball. The respective layers are described in
detail below.
[0030] The core diameter, although not particularly limited, is
generally from 34.9 to 40.3 mm, preferably from 36.1 to 39.4 mm,
and more preferably from 37.3 to 38.5 mm. When the core diameter is
too small, the spin rate on shots with a driver (W#1) may rise, as
a result of which the intended distance may not be achieved. When
the core diameter is too large, the durability to cracking on
repeated impact may worsen, or the feel of the ball at impact may
worsen.
[0031] The core deflection (mm) when compressed under a final load
of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf),
although not particularly limited, is preferably from 3.6 to 4.8
mm, more preferably from 3.7 to 4.4 mm, and even more preferably
from 3.8 to 4.2 mm. When the core is too hard, the spin rate may
rise excessively, resulting in a poor distance, and the feel of the
ball may become too hard. On the other hand, when the core is too
soft, the rebound may be too low, resulting in a poor distance, or
the feel may become too soft and the durability to cracking on
repeated impact may worsen.
[0032] The core surface hardness (Cs), expressed in terms of JIS-C
hardness, is at least 80, preferably from 80 to 90, more preferably
from 81 to 88, and even more preferably from 82 to 86. When the
JIS-C hardness value for the core surface hardness is too high, the
feel of the ball may be too hard or the durability to cracking on
repeated impact may worsen. On the other hand, when this value is
too low, the spin rate rises excessively and the rebound is low,
resulting in a poor distance.
[0033] The core center hardness (Cc), expressed in terms of JIS-C
hardness, is at least 52, preferably from 52 to 63, more preferably
from 53 to 61, and even more preferably from 55 to 59. When the
JIS-C hardness value for the core center hardness is too high, the
spin rate may rise excessively, resulting in a poor distance, or
the feel at impact may be too hard. On the other hand, when this
value is too low, the durability to cracking on repeated impact
worsens and the feel at impact becomes too soft.
[0034] The JIS-C hardness at a position 5 mm from the core center
(C5) is preferably from 54 to 66, more preferably from 56 to 64,
and even more preferably from 58 to 62. The JIS-C hardness at a
position 10 mm from the core center (C10) is preferably from 55 to
68, more preferably from 57 to 66, and even more preferably from 59
to 64. When these hardness values are too high, the spin rate may
rise excessively, resulting in a poor distance, or the feel at
impact may be too hard. On the other hand, when these values are
too low, the durability to cracking on repeated impact may worsen
and the feel at impact may be too soft.
[0035] The above center hardness (Cc) and cross-sectional
hardnesses at specific positions refer to the hardnesses measured
at the center and specific positions on a cross-section obtained by
cutting a golf ball core in half through the center. The surface
hardness (Cs) refers to the hardness measured on the spherical
surface of the core.
[0036] The JIS-C hardness at a position 15 mm from the core center
(C15) is preferably from 68 to 82, more preferably from 70 to 80,
and even more preferably from 72 to 78. When this hardness value is
too high, the feel at impact may become harder and the durability
to cracking under repeated impact may worsen. On the other hand,
when this value is too low, the spin rate may rise excessively and
the rebound may decrease, resulting in a poor distance.
[0037] Next, in this invention, the core satisfies conditions (1)
to (4) below:
20.ltoreq.Cs-Cc, (1)
0<C10-Cc.ltoreq.10, (2)
C10-Cc<Cs-C10, (3)
and
15<Cs-C10 (4)
[0038] In condition (1), the value Cs-Cc is preferably from 21 to
32, more preferably from 23 to 30, and even more preferably from 25
to 28. When this value is too high, the durability to cracking on
repeated impact worsens. On the other hand, when this value is too
low, the spin rate rises excessively and a good distance is not
obtained.
[0039] In condition (2), it is critical for the value C10-Cc to be
higher than 0 and no higher than 10. This means that, in the core
hardness profile of the invention, the gradient from the core
center to a position 10 mm from the center is not very steep. The
C10-Cc value is preferably from 1 to 8, more preferably from 2 to
7, and even more preferably from 3 to 6. At a C10-Cc value outside
of this range, the spin rate on full shots rises and a good
distance is not obtained, or the durability to cracking on repeated
impact worsens.
[0040] In condition (3), it is critical for the value Cs-C10 to be
higher than the value C10-Cc. This means that, in the core hardness
profile of this invention, the gradient is steeper on the outside
than at the core interior. In other words, the value
(Cs-C10)/(C10-Cc) must be higher than 1, and is preferably from 2
to 8, more preferably from 3 to 7, and even more preferably from 4
to 6. When this value is too high, the durability to cracking on
repeated impact worsens. On the other hand, when this value is too
low, the spin rate rises excessively and a good distance is not
obtained.
[0041] In condition (4), it is critical for the value Cs-C10 to be
at least 15. This means that, in the core hardness profile of this
invention, the gradient from a position 10 mm from the core center
(C10) to the core surface (Cs) is steep to a degree that exceeds a
JIS-C hardness of 15. The Cs-C10 value is preferably from 16 to 30,
more preferably from 18 to 28, and even more preferably from 20 to
26. 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, as a result of
which a good distance may not be achieved.
[0042] In addition to above conditions (1) to (4), the core
hardness profile may be suitably adjusted so as to satisfy the
following conditions.
[0043] The value Cs-C15, although not particularly limited, is
preferably from 3 to 14, more preferably from 5 to 12, and even
more preferably from 7 to 10. When this value is too high, the
durability to cracking on repeated impact may worsen. On the other
hand, when this value is too low, the spin rate may rise
excessively, as a result of which a good distance may not be
achieved.
[0044] The value C15-C10, although not particularly limited, is
preferably from 8 to 19, more preferably from 10 to 17, and even
more preferably from 12 to 15. When this value is too high, the
durability to cracking on repeated impact may worsen. On the other
hand, when this value is too low, the spin rate may rise
excessively, as a result of which a good distance may not be
achieved.
[0045] The value C10-C5, although not particularly limited, is
preferably from -1 to 7, more preferably from 0 to 5, and even more
preferably from 1 to 3. When this value is outside of this range,
the spin rate on full shots may rise excessively and a good
distance may not be achieved, or the durability to cracking on
repeated impact may worsen.
[0046] The value C5-Cc, although not particularly limited, is
preferably from 0 to 8, more preferably from 1 to 6, and even more
preferably from 2 to 4. When this value is too high, the spin rate
may rise excessively and a good distance may not be achieved. On
the other hand, when this value is too low, the durability to
cracking on repeated impact may worsen.
[0047] The core having the above hardness profile and deflection is
preferably made of a material that is composed primarily of rubber.
For example, use may be made of a rubber composition obtained by
compounding (A) a base rubber as the chief component, (B) an
organic peroxide, and also a co-crosslinking agent, an inert filler
and, optionally, an organosulfur compound.
[0048] Polybutadiene is preferably used as the base rubber (A). 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.
[0049] Rubber components other than this polybutadiene may be
included in the base rubber (A) 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.
[0050] The organic peroxide (B) 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. A commercially available product may be used as
the organic peroxide. Specific examples include those available
under the trade names Percumyl D, Perhexa C-40, Niper BW and Peroyl
L (all from NOF Corporation), and Luperco 231XL (from Atochem
Co.).
[0051] 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.
[0052] 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 45 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.
[0053] To satisfy the desired hardness profile described above, the
core is preferably formed of a material molded under heat from a
rubber composition which includes, as the essential ingredients:
(A) a base rubber, (B) an organic peroxide, and (C) water and/or a
metal monocarboxylate.
[0054] 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, 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 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.
[0055] Components A and B have already been described above.
[0056] The water serving as component C 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.
[0057] By including a suitable amount of such water, the moisture
content in the rubber composition prior to vulcanization becomes
preferably at least 1,000 ppm, and more preferably at least 1,500
ppm. The upper limit is preferably not more than 8,500 ppm, and
more preferably not more than 8,000 ppm. When the moisture content
of the rubber composition is too low, it may be difficult to obtain
a suitable crosslink density and tan .delta., which may make it
difficult to mold a golf ball having little energy loss and a
reduced spin rate. On the other hand, when the moisture content of
the rubber composition is too high, the core may end up too soft,
which may make it difficult to obtain a suitable core initial
velocity.
[0058] It is also possible to add water directly to the rubber
composition. The following methods (i) to (iii) may be employed to
include water: [0059] (i) applying steam or ultrasonically applying
water in the form of a mist to some or all of the rubber
composition (compounded material); [0060] (ii) immersing some or
all of the rubber composition in water; [0061] (iii) letting some
or all of the rubber composition stand for a given period of time
in a high-humidity environment in a place where the humidity can be
controlled, such as a constant humidity chamber.
[0062] As used herein, "high-humidity environment" is not
particularly limited, so long as it is an environment capable of
moistening the rubber composition, although a humidity of from 40
to 100% is preferred.
[0063] Alternatively, the water may be worked into a jelly state
and added to the above rubber composition. Or a material obtained
by first supporting water on a filler, unvulcanized rubber, rubber
powder or the like may be added to the rubber composition. In such
a form, the workability is better than when water is added directly
to the composition, enabling the efficiency of golf ball production
to be increased. The type of material in which a given amount of
water has been included, although not particularly limited, is
exemplified by fillers, unvulcanized rubbers and rubber powders in
which sufficient water has been included. The use of a material
which causes no loss of durability or resilience is especially
preferred. The moisture content of the above material is preferably
at least 3 wt %, more preferably at least 5 wt %, and even more
preferably at least 10 wt %. The upper limit is preferably not more
than 99 wt %, and even more preferably not more than 95 wt %.
[0064] In this invention, 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.
[0065] 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.
[0066] 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.
[0067] The vulcanized core preferably has a higher moisture content
at the core center than at the core surface. The moisture content
of the molded core can be suitably controlled by adjusting such
conditions as the amount of water included in the rubber
composition, the molding temperature and the molding time.
[0068] The moisture content at the core center, although not
particularly limited, is preferably at least 1,000 ppm, more
preferably at least 1,200 ppm, and even more preferably at least
1,500 ppm. The upper limit is preferably not more than 7,000 ppm,
more preferably not more than 6,000 ppm, and even more preferably
not more than 5,000 ppm. The moisture content at the core surface,
although not particularly limited, is preferably at least 800 ppm,
more preferably at least 1,000 ppm, and even more preferably at
least 1,200 ppm. The upper limit is preferably not more than 5,000
ppm, more preferably not more than 4,000 ppm, and even more
preferably not more than 3,000 ppm. The (moisture content at core
surface)-(moisture content at core center) value is preferably 0
ppm or below, more preferably -100 ppm or below, and even more
preferably -200 ppm or below. The lower limit value is preferably
-1,000 ppm or above, more preferably -700 ppm or above, and even
more preferably -600 ppm or above.
[0069] Measurement of the above moisture content may be carried out
with ordinary instruments. For example, the moisture content can be
measured using the AQ-2100 coulometric Karl Fischer titrator and
the EV-2000 evaporator (both available from Hiranuma Sangyo Co.
Ltd.) at a measurement temperature of 130.degree. C., a preheating
time of 3 minutes and a background measurement time of 30
seconds.
[0070] Letting V.sub.0 be the initial velocity of the core measured
after removing the intermediate layer and cover (which layers are
referred to herein collectively as the "core-covering layers") from
a ball obtained by molding these core-covering layers over the core
and V.sub.60 be the initial velocity of the core measured 60 days
after the day on which V.sub.0 was measured, V.sub.0 is preferably
at least 77.0 m/s, more preferably at least 77.1 m/s, and even more
preferably at least 77.2 m/s, but is preferably not more than 78.5
m/s, more preferably not more than 78.3 m/s, and even more
preferably not more than 78.0 m/s. V.sub.60 is preferably at least
77.0 m/s, and more preferably at least 77.1 m/s, but is preferably
not more than 77.8 m/s, more preferably not more than 77.7 m/s, and
even more preferably not more than 77.6 m/s. When core initial
velocities V.sub.0 and V.sub.60 within the above ranges cannot be
obtained, achieving a satisfactory distance is difficult. Also, if
the core initial velocity is too high, the golf ball may not
conform to the Rules of Golf. Because the core-covering layer
materials are not readily permeable to moisture in the atmosphere,
there are cases where the change in core initial velocity over time
cannot be measured using the ball as is or where it takes a long
time for such change to occur. Therefore, by removing the
core-covering layers and exposing the core itself to the
atmosphere, it is possible to reliably measure the change in core
initial velocity over time.
[0071] The value V.sub.0-V.sub.60 preferably satisfies the
relationship V.sub.0-V.sub.60<0.7, more preferably satisfies the
relationship V.sub.0-V.sub.60<0.6, and still more preferably
satisfies the relationship V.sub.0-V.sub.60<0.5. In this
invention, when moisture has been included in a good balance within
the core, even if the core comes into direct contact with the
atmosphere, it is not readily influenced by the atmospheric
humidity, enabling changes in the core initial velocity to be
suppressed.
[0072] In this invention, the core initial velocity may be 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 may be tested for this purpose in a chamber
at a room temperature of 23.+-.2.degree. C. after being held
isothermally in a 23.+-.1.degree. C. environment for at least 3
hours.
[0073] Next, the method of measuring the dynamic viscoelasticity of
the core is explained. In this invention, letting tan .delta..sub.1
be the loss tangent at a dynamic strain of 1% and tan
.delta..sub.10 be the loss tangent at a dynamic strain of 10% when
the loss tangents are measured at a temperature of -12.degree. C.
and a frequency of 15 Hz in a dynamic viscoelasticity test on
vulcanized rubber at the core center and core surface, and defining
the tan .delta. slope as (tan .delta..sub.10-tan
.delta..sub.1)/(10%-1%), a desirable feature of the invention is
that the difference between the tan .delta. slope at the core
surface and the tan .delta. slope at the core center be larger than
0.002. This difference in slopes is preferably larger than 0.003,
and more preferably larger than 0.004. At a smaller difference in
slope, the energy loss by the core ends up being larger, making a
spin rate-lowering effect more difficult to obtain. Various methods
may be employed to measure the dynamic viscoelastic properties of
the core. For example, a circular disk having a thickness of 2 mm
may be cut out of the cover-encased core by passing through the
geometric center thereof and then, treating this disk as the
sample, using a punching machine to punch out 3 mm diameter
specimens at the places of measurement. In addition, by employing a
dynamic viscoelasticity measuring apparatus (such as that available
under the product name EPLEXOR 500N from GABO) and using a
compression test holder, the tan .delta. values under dynamic
strains of 0.01 to 10% can be measured at an initial strain of 35%,
a measurement temperature of -12.degree. C. and a frequency of 15
Hz, and the slopes determined based on the results of these
measurements.
[0074] Regarding the viscoelastic behavior measured in this way,
there is known to be a correlation between the viscoelastic
behavior in the high-strain region and the spin rate of the golf
ball when struck. Thus, when the tan .delta. in the high-strain
region is relatively large, i.e., when the tan .delta. slope
between a dynamic strain of 10% and a dynamic strain of 1% is
large, the spin rate rises; conversely, when the tan .delta. in the
high-strain region is relatively small, i.e., when the tan .delta.
slope between a dynamic strain of 10% and a dynamic strain of 1% is
small, the spin rate falls. Also, the amount of deformation varies
depending on the club used to strike the golf ball, with
deformation occurring even at the ball center when the ball is
struck with a driver or a middle iron (e.g., a number six iron).
Therefore, when striving to reduce the spin rate on shots with a
driver or a number six iron, good results can be obtained by making
the tan .delta. slope between a dynamic strain of 10% and a dynamic
strain of 1% at the core center small. In cases where the
deformation on impact is small, such as on approach shots near the
green, the influence of the tan .delta. at the core surface is
large. Hence, to increase or maintain the spin rate on approach
shots, good results can be obtained by making the tan .delta. slope
between a dynamic strain of 10% and a dynamic strain of 1% at the
core surface large. Accordingly, to obtain a golf ball that travels
well on shots with a driver and stops on approach shots, what is
desired is for the tan .delta. slope between a dynamic strain of
10% and a dynamic strain of 1% at the core center to be made small
and for the tan .delta. slope between a dynamic strain of 10% and a
dynamic strain of 1% at the core surface to be made large; that is,
for the difference between the tan .delta. slope at the core
surface and the tan .delta. slope at the core center to be made
large.
[0075] In this invention, when the core surface is photographed
with a camera and image data collected by the camera is image
processed in such manner as to identify and digitize scratches
appearing on the core surface, the number of digitized scratches is
preferably 100 or more, and more preferably 200 or more. By
expressing the degree of core surface roughness in terms of the
number of scratches, an attempt is made here to evaluate adhesion
between the core and the intermediate layer encasing the core. This
is based on the observation that the number of scratches on the
core surface has an influence on adhesion between the core and the
intermediate layer. In a core having a small number of such
scratches, the adhesive strength between the core and the
intermediate layer is weak, likely resulting in an inadequate
durability to cracking by the core itself.
[0076] The method of measuring scratches on the core surface is
based on the technology of capturing a photographic image for the
purpose of digitizing the roughness of the core surface as the
number of scratches, and processing the captured image. Use may be
made of, for example, the image processing technique and equipment
described below.
[0077] The measuring equipment setup may include, for example, as
shown in FIG. 3, a stand 50 on which the object to be measured
(i.e., the core) is placed, lighting means 60 situated above the
stand 50, and a camera 70 situated even higher. FIG. 3 also shows a
power supply 90 for the lighting means 60. Individual elements of
the setup are arranged relative to one another in a structure that
can be finely adjusted to provide clear photographic image data for
the core being measured. Enclosing the outer periphery of the
equipment with a blackout curtain or the like is desirable for
minimizing the influence of the outside environment. The image data
captured with the lighting means 60 and camera 70 is imported to a
computer 100, where it is image processed and digitized using
specific image processing software that has been installed in the
computer. Various commercially available products may be used as
the camera, lighting means, computer, image processing software and
the like in the setup shown in FIG. 3. The stand 50 on which the
core is placed and the frame 80 for securing the camera, lighting,
etc. are ordinary structures for which detailed descriptions are
omitted here.
[0078] Using the image processing software, processing is carried
out which, basically, treats regions of the captured image data
that are darker than a threshold setting for brightness and where
there are at least a set number of connected pixels (connectivity
number) in such dark areas (shadows) as scratches, and counts the
number of such scratches. The brightness threshold and the
connectivity number setting used for counting the number of
scratches are made to agree with the depth and size of scratches
generally visible on the core surface. The depth and size of
generally visible scratches are each about 0.5 mm, although these
thresholds and settings may be adjusted as necessary. It is also
possible to classify scratches by the degree of darkness, to
classify the size of scratches by the size of regions of connected
shadows or, from the shape characteristics of connected shadows, to
classify the shape of scratches by prioritizing shapes that are
linear, for example. When carrying out such shape processing,
because the photographed image surface of the core surface is
curved rather than flat, it is preferable to use a dynamic
threshold method.
[0079] Specific commercially available products that may be used as
the image processing equipment and image software (image processing
means) are discussed in the subsequently described examples.
However, because of rapid development recently in image processing
equipment, the equipment mentioned in the examples may not
necessarily be the most suitable. Therefore, it is advisable to
select appropriate equipment in keeping with the core to be
photographed and recent technical advances, and to combine and use
such equipment together.
[0080] In this invention, as mentioned above, by specifying the
roughness of the core surface in terms of a desired number of
scratches, the adhesive strength between the core and the
intermediate layer described below can be increased. Specifically,
based on the method of measuring adhesive strength described in the
examples, the adhesion may be set to preferably at least 1.00 N/4
mm, and more preferably at least 1.15 N/4 mm. In order to achieve a
core surface having such a high adhesion, the core material and
intermediate layer material may be suitably selected and a method
for abrading the core surface may be employed. Abrasion of the core
surface may be carried out using a known method and under known
conditions.
[0081] Next, the intermediate layer is described. The intermediate
layer has a material hardness expressed in terms of Shore D
hardness which, although not particularly limited, is preferably
from 48 to 68, more preferably from 52 to 62, and even more
preferably from 55 to 57. The sphere encased by the intermediate
layer (referred to below as the "intermediate layer-encased
sphere") has a surface hardness, expressed in terms of Shore D
hardness, which is preferably from 55 to 75, more preferably from
59 to 69, and even more preferably from 62 to 64. 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 shots with a putter or on short approaches
may worsen.
[0082] The intermediate layer-encased sphere 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 from 2.8 to 4.0 mm, more preferably from 3.0
to 3.8 mm, and even more preferably from 3.2 to 3.6 mm. When this
value is too high, the feel of the ball may be too soft, the
durability to repeated impact may be poor, or the initial velocity
on full shots may be low, as a result of which the intended
distance may not be achieved. On the other hand, when this value is
too low, the feel of the ball may be too hard and the spin rate on
full shots may rise, as a result of which the intended distance may
not be achieved.
[0083] The intermediate layer has a thickness of preferably from
0.9 to 2.4 mm, more preferably from 1.2 to 2.1 mm, and even more
preferably from 1.5 to 1.8 mm. In this invention, it is preferable
for the thickness of the intermediate layer to be higher than that
of the subsequently described cover (outermost layer). When the
intermediate layer thickness is outside of this range or thinner
than the cover, the spin rate-reducing effects on driver (W#1)
shots may be inadequate, as a result of which a good distance may
not be achieved.
[0084] The intermediate layer material is not particularly limited,
although preferred use can be made of various thermoplastic resin
materials. From the standpoint of fully achieving the desired
effects of the invention, it is especially 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.
[0085] Specifically, a molded material obtained by molding a resin
composition of components (I) to (IV) described below under applied
heat may be used as the highly neutralized resin material.
[0086] Preferred use can be made of the two following components
(I) and (II) as the base resins: [0087] (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 [0088] (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 %.
[0089] The weight-average molecular weight (Mw) of component (I) is
at least 140,000, and preferably at least 145,000. The
weight-average molecular weight (Mw) of component (II) is at least
140,000, and preferably at least 160,000. By thus making these
molecular weights large, the resin material can be assured of
having sufficient resilience.
[0090] 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. In this
invention, 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.
[0091] Here, the weight-average molecular weight (Mw) is a value
calculated relative to polystyrene in gel permeation chromatography
(GPC). A word of explanation is needed here concerning GPC
molecular weight measurement. It is not possible to directly take
GPC measurements for copolymers and terpolymers because these
molecules are adsorbed to the GPC column owing to unsaturated
carboxylic acid groups within the molecules. Instead, the
unsaturated carboxylic acid groups are generally converted to
esters, following which GPC measurement is carried out and the
polystyrene-equivalent average molecular weights Mw and Mn are
calculated.
[0092] The olefins used in component (I) and component (II)
preferably have 2 to 6 carbons, with ethylene being especially
preferred. The unsaturated carboxylic acid used in component (I) is
not particularly limited, although preferred use can be made of
acrylic acid or methacrylic acid. To ensure resilience, the
unsaturated carboxylic acid used in component (II) is acrylic acid.
This is because, when methacrylic acid is used as the unsaturated
carboxylic acid in component (II), the methacrylic acid with its
pendant methyl group may give rise to a buffering action, lowering
the reactivity.
[0093] The unsaturated carboxylic acid content (acid content)
within each of components (I) and (II), although not particularly
limited, is preferably at least 10 wt %, with the upper limit being
preferably less than 15 wt %, and more preferably less than 13 wt
%. When this acid content is low, moldings of the golf ball
material may lack sufficient resilience. On the other hand, when
the acid content is high, the hardness may become excessively high,
adversely affecting the durability.
[0094] The unsaturated carboxylic acid ester used in the terpolymer
serving as component (I) is preferably a lower alkyl ester, with
butyl acrylate (butyl n-acrylate, butyl i-acrylate) being
especially preferred.
[0095] The ester content of the unsaturated carboxylic acid ester
in component (I), in order to employ a resin that is relatively
soft compared with the binary copolymer serving as component (II),
is set to at least 15 wt %, preferably at least 18 wt %, and more
preferably at least 20 wt %, with the upper limit being preferably
not more than 25 wt %. At an ester content higher than this range,
moldings of the intermediate layer material may lack sufficient
resilience. On the other hand, when the ester content is low, the
hardness may increase, adversely affecting the durability.
[0096] The hardness of the base resin (I), that is, the hardness
when the resin itself is molded alone (material hardness),
expressed in terms of Shore D hardness, is preferably at least 30,
and more preferably at least 35, with the upper limit being
preferably not more than 50, and more preferably not more than 45.
The hardness of the base resin (II), that is, the hardness when the
resin itself is molded alone (material hardness), expressed in
terms of Shore D hardness, is preferably at least 40, and more
preferably at least 50, with the upper limit being preferably not
more than 60, and more preferably not more than 57. When base
resins outside of these respective hardness ranges are used, a
material having the desired hardness may not be obtained, or an
adequate resilience and durability may not be obtained.
[0097] In this invention, it is preferable for component (I) and
component (II) to be used together. The mixing proportions of
component (I) and component (II), expressed as the weight ratio
(I):(II), is set to preferably 90:10 to 10:90, more preferably
85:15 to 30:70, and even more preferably 80:20 to 50:50. When the
proportion of component II is higher than this range, the hardness
increases, as a result of which the material may be difficult to
mold.
[0098] When metal neutralization products of resins (i.e.,
ionomers) are used as component (I) and component (II), the type of
metal neutralization product and the degree of neutralization are
not particularly limited. Illustrative examples include 60 mol % Zn
(degree of neutralization with zinc) ethylene-methacrylic acid
copolymers, 40 mol % Mg (degree of neutralization with magnesium)
ethylene-methacrylic acid copolymers, and 40 mol % Mg (degree of
neutralization with magnesium) ethylene-methacrylic acid-acrylic
acid ester terpolymers.
[0099] To ensure at least a given degree of flowability during
injection molding and provide a good molding processability, it is
essential for the melt flow rates of the resins serving as
components (I) and (II) to each be from 0.5 to 20 g/10 min. The
difference between the melt flow rates of components (I) and (II)
is set to not more than 15 g/10 min. When the difference in melt
flow rates between these base resins is too large, the components
cannot be uniformly mixed together during the compounding of
components (I) and (II) in an extruder, and so the mixture becomes
non-uniform, which may lead to injection molding defects.
[0100] 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.).
[0101] 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 even by amateur
golfers. 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+, Me, Ce 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.
[0102] 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 %.
[0103] 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, two 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.
[0104] 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.
[0105] 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.
[0106] 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.
[0107] 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.
[0108] 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.
[0109] 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.
[0110] It is advantageous 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.
[0111] 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.
[0112] Next, the cover, which is the outermost layer of the ball,
is described.
[0113] The cover (outermost layer) has a material hardness
expressed in terms of Shore D hardness which, although not
particularly limited, is preferably from 44 to 58, more preferably
from 48 to 56, and even more preferably from 52 to 54.
[0114] The cover (outermost layer) encased sphere, i.e., the ball,
has a surface hardness expressed in terms of Shore D hardness which
is preferably from 52 to 67, more preferably from 56 to 65, and
even more preferably from 60 to 63. When the cover-encased sphere
is too much softer than this range, the spin rate on driver (W#1)
shots and iron shots may become too high, as a result of which a
good distance may not be obtained. When the cover is too much
harder than this range, the spin rate on approach shots may be
inadequate or the feel at impact may be too hard.
[0115] The cover (outermost layer) encased sphere, that is, the
ball, 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 from 2.4 to 3.7
mm, more preferably from 2.6 to 3.5 mm, and even more preferably
from 2.8 to 3.3 mm. When this value is too high, the feel of the
ball may be too soft, the durability to repeated impact may worsen,
or the initial velocity on full shots may be low, as a result of
which the intended distance may not be achieved. On the other hand,
when this value is too low, the feel of the ball may be too hard
and the spin rate on full shots may rise, as a result of which the
intended distance may not be achieved.
[0116] The cover (outermost layer) has a thickness which, although
not particularly limited, is preferably from 0.3 to 1.5 mm, more
preferably from 0.45 to 1.2 mm, and even more preferably from 0.6
to 0.9 mm. When the cover is thicker than this range, the rebound
on W#1 shots and iron shots may be inadequate and the spin rate may
rise, as a result of which a good distance may not be obtained. On
the other hand, when the cover is thinner than this range, the
scuff resistance may worsen and the ball may lack spin receptivity
on approach shots, resulting in poor controllability.
[0117] The cover (outermost layer) material is not particularly
limited, although the use of any of various types of thermoplastic
resin materials is preferred. For reasons having to do with
controllability and scuff resistance, it is preferable to use a
urethane resin as the cover material of the invention. In
particular, from the standpoint of the mass productivity of
manufactured golf balls, it is preferable to use a cover material
composed primarily of a thermoplastic polyurethane, with formation
more preferably being carried out using a resin blend composed
primarily of (O) a thermoplastic polyurethane and (P) a
polyisocyanate compound.
[0118] In the thermoplastic polyurethane composition containing
above components (O) and (P), to improve the ball properties even
further, a necessary and sufficient amount of unreacted isocyanate
groups should be present in the cover resin material. Specifically,
it is recommended that the combined weight of above components (O)
and (P) be at least 60%, and more preferably at least 70%, of the
weight of the overall cover layer. Components (O) and (P) are
described below in detail.
[0119] The thermoplastic polyurethane (O) 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.
[0120] Any chain extender that has hitherto been employed in the
art relating to thermoplastic polyurethanes may be advantageously
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, an aliphatic diol having 2
to 12 carbons is preferred, and 1,4-butylene glycol is more
preferred, as the chain extender.
[0121] Any polyisocyanate compound hitherto employed in the art
relating to thermoplastic polyurethanes may be advantageously used
without particular limitation as the polyisocyanate compound. For
example, use may be made of one, two 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 reaction 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.
[0122] Commercially available products may be used as the
thermoplastic polyurethane serving as component (O). Illustrative
examples include Pandex T-8295, T-8290, T-8283 and T-8260 (all from
DIC Bayer Polymer, Ltd.).
[0123] Although not an essential ingredient, a thermoplastic
elastomer other than the above thermoplastic polyurethane may be
included as an additional component together with above components
(O) and (P). By including this component (Q) in the above resin
blend, a further improvement in the flowability of the resin blend
can be achieved and the properties required of a golf ball cover
material, such as resilience and scuff resistance, can be
enhanced.
[0124] The relative proportions of above components (O), (P) and
(Q) are not particularly limited. However, to fully elicit the
desirable effects of the invention, the weight ratio (O):(P):(Q) is
preferably from 100:2:50 to 100:50:0, and more preferably from
100:2:50 to 100:30:8.
[0125] In addition to the ingredients making up the thermoplastic
polyurethane, various additives may be optionally included in the
above resin blend. For example, pigments, dispersants,
antioxidants, light stabilizers, ultraviolet absorbers and internal
mold lubricants may be suitably included.
[0126] 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 may be obtained by placing a
molded and vulcanized product composed primarily of a rubber
material as the 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 may be formed over
the intermediate layer by a method that involves encasing the
intermediate sphere with a cover (outermost layer), 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.
[0127] The golf ball of the invention preferably satisfies the
following conditions.
(1) Relationship Between Deflections of Core and Ball Under
Specific Loading
[0128] The relationship between the deflections of the core and the
ball under specific loading is optimized within a specific range.
That is, letting CH be the deflection of the core when compressed
under a final load of 1,275 N (130 kgf) from an initial load of 98
N (10 kgf) and BH be the deflection of the ball when compressed
under a final load of 1,275 N (130 kgf) from an initial load of 98
N (10 kgf), the value CH-BH is preferably from 0.7 to 1.5, more
preferably from 0.9 to 1.3, and even more preferably from 1.0 to
1.2. When this value is too large, the durability to cracking on
repeated impact may worsen, or the feel of the ball on full shots
may be too soft. On the other hand, when this value is too small,
the spin rate on full shots may become too high, as a result of
which the intended distance may not be obtained.
(2) Relationship Between Thicknesses of Intermediate Layer and
Cover
[0129] The relative thicknesses of the intermediate layer and the
cover are set in a specific range. The value obtained by
subtracting the cover thickness from the intermediate layer
thickness is preferably from 0 to 2.0 mm, more preferably from 0.1
to 1.5 mm, and even more preferably from 0.3 to 1.0 mm. When this
value is too large, the feel at impact may become too hard or the
core may become too soft, resulting in a poor durability to
cracking on repeated impact. On the other hand, when this value is
too small, the spin rate on full shots may become too high, as a
result of which the intended distance may not be obtained.
(3) Relationship Between Surface Hardnesses of Ball and
Intermediate Layer-Encased Sphere
[0130] In order for the ball to have a structure in which the cover
is hard on the inside and soft on the outside and the intermediate
layer is hard, it is critical for the surface hardnesses of the
ball and the intermediate layer-encased sphere to satisfy the
relationship: [0131] surface hardness of ball.ltoreq.surface
hardness of intermediate layer-encased sphere. 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 preferably from -20 to
0, more preferably from -15 to -1, and even more preferably from
-10 to -2. When this value is too large, the spin rate on full
shots may rise excessively, as a result of which the intended
distance may not be obtained, or the cover may become hard, giving
the ball an inadequate spin rate in the short game, as a result of
which the controllability may be poor. On the other hand, when this
value is too small, the cover may become too soft, leading to
excessive spin on full shots, or the initial velocity may be too
low, as a result of which the intended distance may not be
achieved.
(4) Relationship Between Surface Hardnesses of Core and Ball
[0132] The relationship between the surface hardnesses of the core
and the ball is optimized within a specific range. That is, the
value obtained by subtracting the surface hardness of the ball from
the surface hardness of the core, expressed in terms of Shore D
hardness, is preferably from -15 to 5, more preferably from -8 to
-4, and even more preferably from -7 to -5. When this value is too
large, the cover may be too hard, making the ball poorly suited for
the short game, or the core may be soft, which may result in a poor
durability to cracking on repeated impact. 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.
(5) Relationship Between Deflections Under Specific Loading of Core
and Intermediate Layer-Encased Sphere
[0133] Letting CH be the deflection of the core when compressed
under a final load of 1,275 N (130 kgf) from an initial load of 98
N (10 kgf) and MH be the deflection of the intermediate
layer-encased sphere when compressed under a final load of 1,275 N
(130 kgf) from an initial load of 98 N (10 kgf), the value CH-MH is
preferably from 0.3 to 1.4, more preferably from 0.5 to 1.2, and
even more preferably from 0.7 to 1.0. When this value is too large,
the durability to cracking on repeated impact may worsen, or the
initial velocity of the ball on full shots may decrease, as a
result of which the intended distance may not be obtained. On the
other hand, when this value is too small, the spin rate on full
shots may become too high, as a result of which the intended
distance may not be obtained.
(6) Relationship Between Surface Hardnesses of Intermediate
Layer-Encased Sphere and Core
[0134] The relationship between the surface hardnesses of the
intermediate layer-encased sphere and the core is optimized within
a specific range. That is, the value obtained by subtracting the
surface hardness of the core from the surface hardness of the
intermediate layer-encased sphere, expressed in terms of Shore D
hardness, is preferably from 3 to 20, more preferably from 5 to 15,
and even more preferably from 7 to 10. When this value is too
large, the durability to cracking under repeated impact may worsen,
or the feel at impact may worsen. On the other hand, when this
value is too small, the spin rate on full shots may be too high, as
a result of which the intended distance may not be obtained.
[0135] Numerous dimples may be formed on the cover (outermost
layer). The number of dimples arranged on the cover surface,
although not particularly limited, is preferably at least 280, more
preferably at least 300, and even more preferably at least 320,
with the upper limit being preferably not more than 360, more
preferably not more than 350, and even more preferably not more
than 340. When the number of dimples is larger than this range, the
ball trajectory becomes lower, as a result of which the distance
may decrease. On the other hand, when the number of dimples is too
small, the ball trajectory becomes higher, as a result of which a
good distance may not be achieved.
[0136] The dimple shapes that are used may be of one type or a
combination of two or more types selected from among 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 about 0.30 mm.
[0137] In order to fully manifest the aerodynamic properties, it is
desirable for the surface coverage ratio of dimples on the
spherical surface of the golf ball, i.e., the ratio SR of the sum
of the individual dimple surface areas, each defined by the flat
plane circumscribed by the edge of a dimple, with respect to the
spherical surface area of the ball were it to have no dimples
thereon, to be set to at least 60% and up to 90%. Also, to optimize
the ball trajectory, it is desirable for the value V.sub.o, 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 up to 0.80. Moreover, it is preferable for the ratio VR of
the sum of the spatial 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 up to
1.0%. Outside of the above ranges in these respective values, the
resulting trajectory may not enable a good distance to be obtained,
and so the ball may fail to travel a fully satisfactory
distance.
[0138] The multi-piece solid golf ball of the invention can be made
to conform to the Rules of Golf for play. Specifically, the
inventive ball may be formed to a diameter which is such that the
ball does not pass through a ring having an inner diameter of
42.672 mm and is not more than 42.80 mm, and to a weight which is
preferably from 45.0 to 45.93 g.
EXAMPLES
[0139] The following Examples and Comparative Examples are provided
to illustrate the invention, and are not intended to limit the
scope thereof.
Examples 1 and 2, Comparative Examples 1 to 7
Formation of Core
[0140] Solid cores for the respective Examples of the invention and
Comparative Examples were produced by preparing the rubber
compositions shown in Table 1 below, then molding and vulcanizing
the compositions under the vulcanization conditions shown in the
same table.
TABLE-US-00001 TABLE 1 Core formulations Example Comparative
Example (pbw) 1 2 1 2 3 4 5 6 7 Polybutadiene A 80 80 80 80 80 80
80 80 80 Polybutadiene B 20 20 20 20 20 20 20 20 20 Zinc acrylate
37.0 34.3 28.5 25.5 23.0 34.3 37.0 28.5 28.5 Organic peroxide (1)
1.0 1.0 1.0 1.0 Organic peroxide (2) 2.5 2.5 2.5 2.5 2.5 Water 0.8
0.8 0.05 0.05 0.05 0.8 0.8 0.05 0.05 Antioxidant 0.1 0.1 0.1 0.1
0.1 0.1 0.1 0.1 0.1 Barium sulfate (1) 15.7 16.8 16.8 11.6 Barium
sulfate (2) 18.2 19.5 20.6 18.2 18.2 Zinc oxide 4.0 4.0 4.0 4.0 4.0
4.0 4.0 4.0 4.0 Zinc salt of 0.6 0.6 0.4 0.4 0.4 0.6 0.6 0.4 0.4
pentachlorothiophenol Vulcanization Temp. 155 155 155 155 155 155
155 155 155 (.degree. C.) conditions Time 15 15 15 15 15 15 15 15
15 (min)
[0141] Details on the ingredients shown in Table 1 are given below.
[0142] Polybutadiene A: Available under the trade name "BR 01" from
JSR Corporation [0143] Polybutadiene B: Available under the trade
name "BR 51" from JSR Corporation [0144] Zinc acrylate: Available
from Nihon Jyoryu Co., Ltd. [0145] Organic peroxide (1): Dicumyl
peroxide, available under the trade name "Percumyl D" from NOF
Corporation [0146] 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 [0147] Water:
Distilled water, from Wako Pure Chemical Industries, Ltd. [0148]
Antioxidant: 2,2'-Methylenebis(4-methyl-6-butylphenol), available
under the trade name "Nocrac NS-6" from Ouchi Shinko Chemical
Industry Co., Ltd. [0149] Barium sulfate (1): Available under the
trade name "Barico #300" from Hakusui Tech [0150] Barium sulfate
(2): Available as "Precipitated Barium Sulfate #100" from Sakai
Chemical Co., Ltd. [0151] Zinc oxide: Available under the trade
name "Zinc Oxide Grade 3" from Sakai Chemical Co., Ltd. [0152] Zinc
stearate: Available under the trade name "Zinc Stearate G" from NOF
Corporation [0153] Sulfur: Available under the trade name
"Sulfax-5" from Tsurumi Chemical Industry Co., Ltd.
Formation of Intermediate Layer and Cover
[0154] 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
materials formulated as shown in Table 2, a cover (outermost layer)
was injection-molded over the resulting intermediate layer-encased
sphere, thereby producing a golf ball having an intermediate layer
and a cover (outermost layer) over the core. Although not shown in
the diagram, a common dimple pattern was formed on the surface of
the ball in each of the Examples of the invention and the
Comparative Examples.
TABLE-US-00002 TABLE 2 Resin materials (pbw) I II III T-8295 75 100
T-8290 25 Surlyn 9320 10 AN 4221C 90 Hytrel 4001 11 11 Titanium
oxide 3.9 3.9 Polyethylene wax 1.2 1.2 Isocyanate compound 7.5 7.5
Magnesium stearate 60 Magnesium oxide 2.1 Polytail H 8
[0155] Details on the materials shown in Table 2 are as follows.
[0156] T-8295, T-8290: MDI-PTMG type thermoplastic polyurethanes
available from DIC Bayer Polymer under the trademark Pandex. [0157]
Surlyn 9320: An ethylene-methacrylic acid-acrylic acid ester
terpolymer available from E.I. DuPont de Nemours & Co. [0158]
AN 4221C: An unneutralized ethylene-acrylic acid copolymer
available from DuPont-Mitsui Polychemicals Co., Ltd. [0159] Hytrel
4001: A polyester elastomer available from DuPont-Toray Co., Ltd.
[0160] Polyethylene wax: Available as "Sanwax 161P" from Sanyo
Chemical Industries, Ltd. [0161] Isocyanate compound:
4,4'-Diphenylmethane diisocyanate [0162] Magnesium oxide: "Kyowamag
MF 150" from Kyowa Chemical Industry Co., Ltd. [0163] Polytail H:
Available from Mitsubishi Chemical Corporation
[0164] For each of the resulting golf balls, properties such as the
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 3. In addition, the flight performance, properties on
approach shots, feel, and scuff resistance for each golf ball were
evaluated as described below. Those results are shown in Table
4.
Core Hardness Profile
[0165] 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.
[0166] 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.
[0167] The Shore D hardness at the core surface was measured with a
type D durometer in accordance with ASTM D2240-95.
Dynamic Viscoelastic Properties of Core
[0168] A circular disk having a thickness of 2 mm was cut out by
passing through the geometric center of the core and, treating the
core center and surface vicinity on this disk as the respective
samples, a punching machine was used to punch out 3 mm diameter
specimens at the places of measurement. The loss tangents (tan
.delta.) under dynamic strains of from 0.01% to 10% were measured
at an initial strain of 35%, a measurement temperature of
-12.degree. C. and a frequency of 15 Hz using a dynamic
viscoelasticity measuring apparatus (such as that available under
the product name EPLEXOR 500N from GABO) and a compression test
holder. Measurement results obtained within a radius of 5 mm from
the core center were treated as the tan .delta. at the core center,
and measurement results within 5 mm of the core surface were
treated as the tan .delta. at the core surface.
Core Moisture Content
[0169] Using the AQ-2100 coulometric Karl Fischer titrator and the
EV-2000 evaporator (both available from Hiranuma Sangyo Co., Ltd.),
measurement of the moisture content was carried out at a
measurement temperature of 130.degree. C., a preheating time of 3
minutes and a background measurement time of 30 seconds. The
interval time was set to 99 seconds and the current was set to
"Fast." Measurement results obtained within a radius of 5 mm from
the core center were treated as the moisture content for the center
of the core, and measurement results obtained within 5 mm of the
core surface were treated as the moisture content for the surface
of the core.
Initial Velocity of Core after Standing
[0170] A core was prepared by peeling the intermediate layer and
cover from a golf ball. The core initial velocity measured on the
day that the core-covering layers--these being the intermediate
layer and cover--were peeled off was treated as the Day 0 result,
and the initial core velocity when 60 days had elapsed thereafter
was treated as the Day 60 result. During this time, the core was
kept in a chamber controlled to a temperature of 24.degree. C. and
40% humidity. 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.+-.2.degree. C. after being held isothermally in a
23.+-.1.degree. C. environment for at least 3 hours. Twenty cores
were each hit twice. The time taken for the core to traverse a
distance of 6.28 ft (1.91 m) was measured and used to compute the
initial velocity. This cycle was carried out over a period of about
15 minutes.
Core Surface Roughness
[0171] A grinding wheel was mounted on a centerless grinder
commonly used for grinding spheres and the core surface was abraded
for 5 seconds at 2,500 rpm, following which the surface roughness
of the core was determined by the following method. An
electrodeposited diamond wheel (40/50 grit) was used as the
grinding wheel in Examples 1 and 2 of the invention and in
Comparative Examples 1 to 5, and a common grinding wheel (GC 46)
differing in the frequency of use was used in Comparative Examples
6 and 7. Core surface data was collected from an area having a
diameter of about 10 mm at each of five places and the data for
each subjected to image processing, thereby obtaining the number of
scratches on the core surface. Next, using the average value for
the five places as the measured value for a single ball, the
average value for five balls (N=5) was determined. The measurement
apparatus and method were as shown in FIG. 3 and described above.
The following commercial equipment was used in the apparatus shown
in FIG. 3.
Lighting means 60: UV LED lamp (LDR2-60VL385-BTTPTK), from CCS Inc.
Lighting power source 90: PD3-3024-3-PI, also from CCS Inc. Camera
70: Sony XC-73 CCD camera Computer 100: A PC using Windows.TM. 7 as
the operating system, and HALCON sold by LinX Corporation as the
image processing software FIG. 4 is an image showing part of the
core surface obtained by image processing with the above image
processing software. Non-black regions are shadows; because these
are regions darker than a threshold setting, they basically
indicate scratches. In the processing carried out in the practice
of the invention, regions of 30 or more connected pixels were
counted as scratches; the number of scratches in this image is
considered to be 95. In FIG. 4, regions that appear as dots do not
satisfy the connectivity number setting (here, an unbroken sequence
of 30 pixels), and so are not included in the number of
scratches.
Bond Strength (Peel Value) Between Core and Intermediate Layer
[0172] Referring to FIG. 2, in a sphere composed of a core 1
encased by an intermediate layer 2, two parallel cuts 11, 12 spaced
4.0 mm apart were made in the intermediate layer 2 in such a way as
to pass entirely through this layer, and the intermediate layer 2
at both ends of the sphere was peeled off. Next, a lateral cut 13
that passes entirely through the intermediate layer 2 was made at a
right angle to the first two cuts 11, 12, after which the bond
strength was measured by immobilizing the core portion 1 and
pulling on the cut end of the intermediate layer 2. Measurement was
carried out using an Instron tester and based on JIS K6256
("Adhesion Test Method for Vulcanized Rubber and Thermoplastic
Rubber"). Using the specially prepared test specimen described
above, the clamp was moved at a speed of 50 mm/min and the tensile
strength was measured at 0.1 mm intervals. The average of the
tensile strengths for three test specimens, after discarding the
first quarter and the last quarter of all the measurement points,
was treated as the bond strength (units: N).
Diameter of Core or Intermediate Layer-Encased Sphere
[0173] 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 measured cores or intermediate layer-encased spheres was
determined.
Ball Diameter
[0174] 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.
Deflection of Core, Intermediate Layer-Encased Sphere and Ball
[0175] A core, intermediate layer-encased sphere or ball was 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) 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. In the table, letting A be the core
deflection, B be the deflection by the intermediate layer-encased
sphere and C be the ball deflection, the values A-B and A-C were
calculated.
Material Hardnesses of Intermediate Layer and Cover (Shore D
Hardnesses)
[0176] 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)
[0177] 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.
TABLE-US-00003 TABLE 3 Example Comparative Example 1 2 1 2 3
Structure 3-piece 3-piece 3-piece 3-piece 3-piece Core Diameter
(mm) 37.7 37.7 37.7 37.7 37.7 Weight (g) 32.9 32.9 32.7 32.7 32.7
Deflection A (mm) 3.9 4.2 3.8 4.2 4.8 Hardness profile (JIS-C)
Surface hardness (Cs) 85 82 82 79 75 Hardness at position 76 73 72
69 66 15 mm from center (C15) Hardness at position 62 60 69 65 61
10 mm from center (C10) Hardness at position 61 59 69 65 61 5 mm
from center (C5) Center hardness (Cc) 57 56 61 59 56 Cs - C15 8 9 9
10 9 C15 - C10 14 13 3 4 4 C10 - C5 2 1 0 0 0 C5 - C0 3 3 8 6 5 Cs
- C10 22 22 13 13 13 C10 - Cc 5 4 8 6 5 (Cs - C10)/(C10 - Cc) 4.4
5.5 1.6 2.1 2.6 Surface - Center (Cs - Cc) 27 26 21 20 19 Surface
hardness (Shore D) 56 54 54 52 49 tan .delta. at 0.1% strain 0.0420
0.0400 0.0440 0.0420 0.0420 core center 1% strain 0.0450 0.0440
0.0460 0.0430 0.0460 10% strain 0.0580 0.0550 0.1000 0.1070 0.1050
tan .delta. slope for 0.0014 0.0012 0.0060 0.0071 0.0066 10% strain
and 1% strain tan .delta. at 0.1% strain 0.0730 0.0690 0.0750
0.0750 0.0770 core surface 1% strain 0.0750 0.0720 0.0790 0.0780
0.0800 10% strain 0.1320 0.1350 0.1400 0.1480 0.1440 tan .delta.
slope for 0.0063 0.0070 0.0068 0.0078 0.0071 10% strain and 1%
strain Difference in tan .delta. slopes 0.0049 0.0058 0.0008 0.0007
0.0006 Core Center (ppm) 2020 1980 992 1059 1017 moisture Surface
(ppm) 1802 1827 1795 1845 1833 content Surface - Center (ppm) -218
-153 803 786 816 Initial Day 0 of standing (V0), m/s 77.69 77.45
77.63 77.36 77.18 velocity of Day 60 of standing (V60), m/s 77.29
77.03 76.88 76.64 76.47 core after Initial velocity 0.40 0.42 0.75
0.72 0.71 standing difference (V0 - V60), m/s Core surface Number
of scratches 220 245 280 305 315 roughness Core and Peel value (N/4
mm) 1.12 1.18 1.31 1.32 1.34 intermediate layer Intermediate
Material I I I I I layer Thickness (mm) 1.7 1.7 1.7 1.7 1.7
Specific gravity 0.95 0.95 0.95 0.95 0.95 Material hardness (Shore
D) 56 56 56 56 56 Intermediate Diameter (mm) 41.1 41.1 41.1 41.1
41.1 layer-encased Weight (g) 40.8 40.8 40.6 40.6 40.6 sphere
Deflection B (mm) 3.3 3.5 3.3 3.7 4.1 Surface hardness (Shore D) 63
63 63 63 63 Intermediate layer surface hardness - 7 9 9 11 14 Core
surface hardness (Shore D) Deflection difference (A - B) 0.7 0.7
0.5 0.5 0.7 Cover Material II II II II II Thickness (mm) 0.8 0.8
0.8 0.8 0.8 Specific gravity 1.12 1.12 1.12 1.12 1.12 Material
hardness (Shore D) 53 53 53 53 53 Ball Diameter (mm) 42.7 42.7 42.7
42.7 42.7 Weight (g) 45.6 45.6 45.3 45.4 45.3 Deflection C (mm) 2.9
3.2 2.9 3.3 3.7 Surface hardness (Shore D) 61 61 61 61 61 Core
surface hardness - -5 -7 -7 -9 -12 Ball surface hardness (Shore D)
Ball surface hardness - Intermediate -2 -2 -2 -2 -2 layer surface
hardness (Shore D) Intermediate layer thickness - Cover thickness
(mm) 0.9 0.9 0.9 0.9 0.9 Deflection difference (A - C) 1.0 1.1 0.8
0.9 1.1 Comparative Example 4 5 6 7 Structure 3-piece 3-piece
3-piece 3-piece Core Diameter (mm) 37.7 37.7 37.7 37.7 Weight (g)
32.5 32.3 32.7 32.7 Deflection A (mm) 4.2 3.9 3.8 3.8 Hardness
profile (JIS-C) Surface hardness (Cs) 82 85 82 82 Hardness at
position 73 76 72 72 15 mm from center (C15) Hardness at position
60 62 69 69 10 mm from center (C10) Hardness at position 59 61 69
69 5 mm from center (C5) Center hardness (Cc) 56 57 61 61 Cs - C15
9 8 9 9 C15 - C10 13 14 3 3 C10 - C5 1 2 0 0 C5 - C0 3 3 8 8 Cs -
C10 22 22 13 13 C10 - Cc 4 5 8 8 (Cs - C10)/(C10 - Cc) 5.5 4.4 1.6
1.6 Surface - Center (Cs - Cc) 26 27 21 21 Surface hardness (Shore
D) 54 56 54 54 tan .delta. at 0.1% strain 0.0400 0.0420 0.0440
0.0440 core center 1% strain 0.0440 0.0450 0.0460 0.0460 10% strain
0.0550 0.0580 0.1000 0.1000 tan .delta. slope for 0.0012 0.0014
0.0060 0.0060 10% strain and 1% strain tan .delta. at 0.1% strain
0.0690 0.0730 0.0750 0.0750 core surface 1% strain 0.0720 0.0750
0.0790 0.0790 10% strain 0.1350 0.1320 0.1400 0.1400 tan .delta.
slope for 0.0070 0.0063 0.0068 0.0068 10% strain and 1% strain
Difference in tan .delta. slopes 0.0058 0.0049 0.0008 0.0008 Core
Center (ppm) 1980 2020 992 992 moisture Surface (ppm) 1827 1802
1795 1795 content Surface - Center (ppm) -153 -218 803 803 Initial
Day 0 of standing (V0), m/s 77.45 77.69 77.63 77.63 velocity of Day
60 of standing (V60), m/s 77.03 77.29 76.88 76.88 core after
Initial velocity 0.42 0.40 0.75 0.75 standing difference (V0 -
V60), m/s Core surface Number of scratches 245 220 110 90 roughness
Core and Peel value (N/4 mm) 1.18 1.12 0.74 0.59 intermediate layer
Intermediate Material I I I I layer Thickness (mm) 1.7 1.0 1.7 1.7
Specific gravity 0.95 0.95 0.95 0.95 Material hardness (Shore D) 56
56 56 56 Intermediate Diameter (mm) 41.1 39.7 41.1 41.1
layer-encased Weight (g) 40.4 36.8 40.6 40.6 sphere Deflection B
(mm) 3.5 3.5 3.3 3.3 Surface hardness (Shore D) 63 63 63 63
Intermediate layer surface hardness - 9 7 9 9 Core surface hardness
(Shore D) Deflection difference (A - B) 0.7 0.4 0.5 0.5 Cover
Material III II II II Thickness (mm) 0.8 1.5 0.8 0.8 Specific
gravity 1.12 1.12 1.12 1.12 Material hardness (Shore D) 56.5 53 53
53 Ball Diameter (mm) 42.7 42.7 42.7 42.7 Weight (g) 45.1 45.6 45.3
45.3 Deflection C (mm) 3.1 3.0 2.9 2.9 Surface hardness (Shore D)
64 60 61 61 Core surface hardness - -10 -4 -7 -7 Ball surface
hardness (Shore D) Ball surface hardness - Intermediate 1 -3 -2 -2
layer surface hardness (Shore D) Intermediate layer thickness -
Cover thickness (mm) 0.9 -0.5 0.9 0.9 Deflection difference (A - C)
1.1 0.9 0.8 0.8
[0178] In addition, the flight performance (W#1), spin performance
on approach shots, feel, scuff resistance, and durability to
cracking 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
4.
Flight Performance on Shots with a Driver
[0179] A driver (W#1) was mounted on a golf swing robot, the
distance traveled by the ball when struck at a head speed (HS) of
45 m/s was measured, and the flight performance was rated according
to the criteria shown below. The club used was a TourStage X-Drive
709 D430 driver (2013 model; loft angle, 9.5.degree.) manufactured
by Bridgestone Sports Co., Ltd. The above head speed corresponds to
the average head speed of mid- and high-level amateur golfers.
[0180] Rating Criteria: [0181] Good: Total distance was 233.0 m or
more [0182] NG: Total distance was less than 233.0 m
Spin Performance on Approach Shots
[0183] 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 rated
according to the following criteria.
[0184] Rating Criteria: [0185] Good: Spin rate was 5,700 rpm or
more [0186] Fair: Spin rate was at least 5,600 rpm but less than
5,700 rpm [0187] NG: Spin rate was less than 5,600 rpm
Feel
[0188] 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.
[0189] Rating Criteria: [0190] Good: Six or more out of ten golfers
rated the feel as good [0191] Fair: Three to five out of ten
golfers rated the feel as good [0192] NG: Two or fewer out of ten
golfers rated the feel as good
[0193] Here, a "good feel" refers to a feel at impact that is
appropriately soft.
Scuff Resistance
[0194] A non-plated pitching sand wedge was set in a swing robot
and the ball was hit once at a head speed of 35 m/s, following
which the surface state of the ball was visually examined and rated
as follows.
[0195] Rating Criteria: [0196] Good: The ball was judged to be
still capable of use. [0197] NG: The ball was judged to be no
longer capable of use.
Durability to Cracking
[0198] The same type of driver (W#1) as in the flight performance
evaluation was mounted on a golf swing robot and the ball was
repeatedly struck at a head speed of 45 m/s. For the ball in each
Example, a loss of durability was judged to have occurred when the
initial velocity of the ball fell to or below 97% of the average
initial velocity for the first ten shots. The average value for
three measured golf balls (N=3) was used as the basis for
evaluation in each Example. The 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, and the durability was rated according to the following
criteria.
[0199] Rating Criteria: [0200] Good: Durability index was 90 or
more [0201] Fair: Durability index was at least 80 but less than 90
[0202] NG: Durability index was less than 80
TABLE-US-00004 [0202] TABLE 4 Example Comparative Example 1 2 1 2 3
4 5 6 7 Flight W#1 Spin rate 2,788 2,728 2,878 2,813 2,698 2,671
2,938 2,878 2,878 HS, 45 m/s (rpm) Total 234.4 233.8 232.3 231.6
230.4 234.8 230.1 232.3 232.3 distance (m) Rating good good NG NG
NG good NG NG NG Performance Spin rate 5,824 5,724 5,788 5,729
5,669 5,588 5,879 5,788 5,788 on approach (rpm) shots Rating good
good good good fair NG good good good Feel Rating good good good
good good good good good good Scuff Rating good good good good good
good good good good resistance Durability Rating good good good
good good good good fair NG to cracking
[0203] In Comparative Example 1, the hardness profile of the core
fell outside the range in values for the invention. As a result,
the spin rate rose on full shots with a driver (W#1) and a good
distance was not achieved.
[0204] In Comparative Example 2, the hardness profile of the core
fell outside the range in values for the invention. As a result,
the spin rate rose on full shots with a driver and a good distance
was not achieved.
[0205] In Comparative Example 3, the hardness profile of the core
fell outside the range in values for the invention, making the core
soft and holding down the spin rate on W#1 shots. As a result, the
initial velocity of the ball when struck was low and a good
distance was not achieved.
[0206] The ball in Comparative Example 4 had a cover that was
harder than the intermediate layer. As a result, the spin rate of
approach shots was insufficient, making the ball performance
inferior in the short game.
[0207] The ball in Comparative Example 5 had a cover (outermost
layer) that was thicker than the intermediate layer. As a result,
on W#1 shots, the spin rate rose and a good distance was not
achieved.
[0208] In Comparative Example 6, the hardness profile of the core
fell outside the range of values for the invention. As a result,
the spin rate on full shots with a driver (W#1) rose and a good
distance was not achieved.
[0209] In Comparative Example 7, the hardness profile of the core
fell outside the range of values for the invention. As a result,
the spin rate on full shots with a driver (W#1) rose and a good
distance was not achieved. Also, the number of scratches on the
core surface was small and the durability to cracking was low.
[0210] Japanese Patent Application No. 2015-113941 is incorporated
herein by reference.
[0211] 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.
* * * * *