U.S. patent application number 15/137299 was filed with the patent office on 2016-12-15 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, Hideo WATANABE.
Application Number | 20160361605 15/137299 |
Document ID | / |
Family ID | 57516626 |
Filed Date | 2016-12-15 |
United States Patent
Application |
20160361605 |
Kind Code |
A1 |
WATANABE; Hideo ; et
al. |
December 15, 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 (initial
velocity of intermediate layer-encased sphere)/(initial velocity of
core).gtoreq.0.995. Also, the core, the intermediate layer-encased
sphere and the ball have respective deflections under given
compression conditions which satisfy a specific condition. When
used by golfers whose head speed is not very fast, the ball
achieves a good distance on shots with a driver, in addition to
which it has a soft feel and is able to retain a high spin
performance on approach shots.
Inventors: |
WATANABE; Hideo;
(Chichibushi, JP) ; KIMURA; Akira; (Chichibushi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bridgestone Sports Co., Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
Bridgestone Sports Co.,
Ltd.
Tokyo
JP
|
Family ID: |
57516626 |
Appl. No.: |
15/137299 |
Filed: |
April 25, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A63B 37/0033 20130101;
A63B 37/0084 20130101; A63B 37/0092 20130101; A63B 37/0032
20130101; A63B 37/0044 20130101; A63B 37/0063 20130101; A63B
37/0077 20130101; A63B 37/0039 20130101; A63B 37/0062 20130101;
A63B 37/0046 20130101; A63B 37/0043 20130101; A63B 37/0045
20130101; A63B 37/0075 20130101; A63B 37/004 20130101; A63B 37/0065
20130101; A63B 37/0087 20130101; A63B 37/0031 20130101; A63B
37/0068 20130101 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 11, 2015 |
JP |
2015-118026 |
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: (Shore D hardness at ball
surface).ltoreq.(Shore D hardness at surface of intermediate
layer-encased sphere); (1) the intermediate layer and the cover
have respective thicknesses which satisfy the relationship: cover
thickness.ltoreq.intermediate layer thickness; (2) the intermediate
layer-encased sphere and the core have respective initial
velocities which satisfy the relationship: (initial velocity of
intermediate layer-encased sphere)/(initial velocity of
core).gtoreq.0.995; and (3) the core, the intermediate
layer-encased sphere and the ball, when compressed under a final
load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf),
have respective deflections (mm) A, B and C which satisfy the
condition: A+B+C.gtoreq.11.5, (4) with the proviso that
A.gtoreq.4.0 and C.gtoreq.3.2.
2. The golf ball of claim 1 which, in formula (3), satisfies the
condition: (initial velocity of intermediate layer-encased
sphere)/(initial velocity of core).gtoreq.1.004.
3. The golf ball of claim 1 which, in formula (4), satisfies the
condition (A-C).gtoreq.0.9.
4. The golf ball of claim 1 wherein the core has a hardness profile
which, expressed in terms of JIS-C hardness, satisfies conditions
(i) to (vi) 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:
18.ltoreq.Cs-Cc, (i) 0<C10-Cc.ltoreq.10, (ii) C10-Cc<Cs-C10,
(iii) 10<Cs-C10, (iv) Cs.gtoreq.68, and (v) Cc.gtoreq.48
(vi).
5. The golf ball of claim 1 which further satisfies condition
(iii-a) below: (Cs-C10)/(C10-Cc).gtoreq.1.0 (iii-a).
6. The golf ball of claim 1 which further satisfies condition (vii)
below: Cs-Cc<10 (vii).
7. The golf ball of claim 1, wherein the intermediate layer is
formed of a material obtained by blending as essential components:
100 parts by weight of a resin component comprising, in admixture,
a base resin of (a) an olefin-unsaturated carboxylic acid random
copolymer and/or a metal ion neutralization product of an
olefin-unsaturated carboxylic acid random copolymer mixed with (b)
an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid
ester random terpolymer and/or a metal ion neutralization product
of an olefin-unsaturated carboxylic acid-unsaturated carboxylic
acid ester random terpolymer in a weight ratio between 100:0 and
0:100, and (e) a non-ionomeric thermoplastic elastomer in a weight
ratio between 100:0 and 50:50; (c) 5 to 80 parts by weight of a
fatty acid and/or fatty acid derivative having a molecular weight
of from 228 to 1,500; and (d) 0.1 to 17 parts by weight of a basic
inorganic metal compound capable of neutralizing un-neutralized
acid groups in the base resin and component (c).
8. The golf ball of claim 1, wherein the ball, the intermediate
layer-encased sphere and the core have respective initial
velocities which satisfy the relationship: initial velocity of
ball<initial velocity of core<initial velocity of envelope
layer-encased sphere (5).
9. The golf ball of claim 1 which, in formula (1), satisfies the
condition: (Shore D hardness at surface of intermediate
layer-encased sphere).gtoreq.(Shore D hardness at core surface)
(1').
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. 2015-118026 filed in
Japan on Jun. 11, 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] Many golf balls that improve the flight performance on full
shots with a driver (W#1) by amateur golfers whose head speed is
not very fast have hitherto been disclosed. For example, art which
relates to golf balls of two or more pieces having a core and a
cover or to multi-piece solid golf balls of three or more pieces
having a core, an intermediately layer and a cover, and which is
focused on the hardness profile in the core, the hardness
relationship between the intermediate layer and the cover, and the
intermediate layer material has been disclosed. Such golf balls are
described in, for example, JP-A 2014-187351, JP-A 2011-120898, JP-A
2010-214105, JP-A 2010-172702, JP-A 2008-194474 and JP-A
2008-194473.
[0004] Yet, there remains room for improvement in achieving an
increased distance in such golf balls. To achieve not only an
increased distance, but also further increase the enjoyability of
the game, it is desired that a high spin performance on approach
shots be retained. In addition, it is also desired that the ball
have a good durability when repeatedly struck.
SUMMARY OF THE INVENTION
[0005] It is therefore an object of this invention to provide a
multi-piece solid golf ball which, while maintaining a good
distance on shots with a driver (W#1) by an amateur golfer whose
head speed is not very fast, is able to retain a high spin
performance on approach shots.
[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 providing the ball with a
construction such that it has both a specific relationship between
the surface hardness of a sphere composed of the core peripherally
encased with the intermediate layer (intermediate layer-encased
sphere) and the surface hardness of the ball and also a specific
relationship between the thickness of the intermediate layer and
the thickness of the cover, such that the initial velocity of the
intermediate layer-encased sphere and the initial velocity of the
core satisfy the condition (initial velocity of intermediate
layer-encased sphere)/(initial velocity of core).gtoreq.0.995, and
moreover such that, letting the deflections (mm) of the core,
intermediate layer-encased sphere and ball when compressed under a
final load of 1,275 N (130 kgf) from an initial load of 98 N (10
kgf) be respectively A, B and C, the condition A+B+C.gtoreq.11.5
(with the proviso that A.gtoreq.4.0 and C.gtoreq.3.2) is satisfied,
the spin rate of the ball on full shots with a driver (W#1),
particularly by an amateur golfer having a head speed of 35 m/s or
less, can be kept low, enabling an increased distance to be
achieved, and yet the ball is able to retain a high spin
performance on approach shots. As a result, we have succeeded in
developing a superior golf ball which provides good enjoyability in
the game of golf. We have found, moreover, that this golf ball has
a soft feel on full shots with a driver (W#1) and a good durability
when repeatedly struck. As used herein, "amateur golfer" refers in
particular to a player having a head speed (HS) of 35 m/s or
less.
[0007] Accordingly, the invention provides a multi-piece solid golf
having a core, a cover and an intermediate layer therebetween,
wherein a sphere composed 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:
(Shore D hardness at ball surface).ltoreq.(Shore D hardness at
surface of intermediate layer-encased sphere); (1)
the intermediate layer and the cover have respective thicknesses
which satisfy the relationship:
cover thickness.ltoreq.intermediate layer thickness; (2)
the intermediate layer-encased sphere and the core have respective
initial velocities which satisfy the relationship:
(initial velocity of intermediate layer-encased sphere)/(initial
velocity of core).gtoreq.0.995; and (3)
the core, the intermediate layer-encased sphere and the ball, when
compressed under a final load of 1,275 N (130 kgf) from an initial
load of 98 N (10 kgf), have respective deflections (mm) A, B and C
which satisfy the condition:
A+B+C.gtoreq.11.5, (4)
with the proviso that A.gtoreq.4.0 and C.gtoreq.3.2.
[0008] In a preferred embodiment, the golf ball, in formula (3),
satisfies the condition:
(initial velocity of intermediate layer-encased sphere)/(initial
velocity of core).gtoreq.1.004.
[0009] In another preferred embodiment, the golf ball, in formula
(4), satisfies the condition (A-C).gtoreq.0.9.
[0010] The core preferably has a hardness profile which, expressed
in terms of JIS-C hardness, satisfies conditions (i) to (vi) 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:
18.ltoreq.Cs-Cc, (i)
0<C10-Cc.ltoreq.10, (ii)
C10-Cc<Cs-C10, (iii)
10<Cs-C10, (iv)
Cs.gtoreq.68, and (v)
Cc.gtoreq.48. (vi)
[0011] In another preferred embodiment, the golf ball further
satisfies condition (iii-a) below:
(Cs-C10)/(C10-Cc).gtoreq.1.0. (iii-a)
[0012] In yet another preferred embodiment, the golf ball further
satisfies condition (vii) below:
Cs-Cc<10. (vii)
[0013] The intermediate layer is preferably formed of a material
obtained by blending as essential components: 100 parts by weight
of a resin component comprising, in admixture, [0014] a base resin
of (a) an olefin-unsaturated carboxylic acid random copolymer
and/or a metal ion neutralization product of an olefin-unsaturated
carboxylic acid random copolymer mixed with (b) an
olefin-unsaturated carboxylic acid-unsaturated carboxylic acid
ester random terpolymer and/or a metal ion neutralization product
of an olefin-unsaturated carboxylic acid-unsaturated carboxylic
acid ester random terpolymer in a weight ratio between 100:0 and
0:100, and [0015] (e) a non-ionomeric thermoplastic elastomer in a
weight ratio between 100:0 and 50:50; (c) 5 to 80 parts by weight
of a fatty acid and/or fatty acid derivative having a molecular
weight of from 228 to 1,500; and (d) 0.1 to 17 parts by weight of a
basic inorganic metal compound capable of neutralizing
un-neutralized acid groups in the base resin and component (c).
[0016] In a further preferred embodiment, the ball, the
intermediate layer-encased sphere and the core have respective
initial velocities which satisfy the relationship:
initial velocity of ball<initial velocity of core<initial
velocity of envelope layer-encased sphere. (5)
[0017] In a still further preferred embodiment, the golf ball, in
formula (1), satisfies the condition:
(Shore D hardness at surface of intermediate layer-encased
sphere).gtoreq.(Shore D hardness at core surface). (1')
Advantageous Effects of the Invention
[0018] The multi-piece solid golf ball of the invention, when
played by a golfer whose head speed is not very fast (particularly
a golfer having a head speed of 35 m/s or less), is able to achieve
a good distance on shots with a driver (W#1) and also can provide a
soft feel. Moreover, this golf ball is able to retain a high spin
performance on approach shots and has a good durability to repeated
impact.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0019] FIG. 1 is a schematic sectional diagram of a golf ball
according to an embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The objects, features and advantages of the invention will
become more apparent from the following detailed description, taken
in conjunction with the foregoing diagram.
[0021] 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.
[0022] 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 obtained. 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.
[0023] 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 4.0 to 5.3
mm, more preferably from 4.1 to 5.1 mm, and even more preferably
from 4.3 to 4.9 mm. When this value is too high, the feel of the
ball at impact may be too soft and the durability on repeated
impact may worsen, or the initial velocity 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 low, the feel
of the ball becomes too hard and the spin rate on full shots rises,
as a result of which the intended distance is not achieved.
[0024] Next, in the core hardness profile, the specific hardness
range differs for cases where the hardness difference between the
surface and center of the core, expressed in terms of JIS-C
hardness, is 15 or more and for cases where this hardness
difference is 10 or less. The details are as follows.
I. JIS-C Hardness Difference Between Core Surface and Center
.gtoreq.15
[0025] This core hardness profile has a hardness state with no
gradient from the core center to a specific cross-sectional
position but with a steep gradient from a specific cross-sectional
position to the surface, and is able, in particular, to fully
achieve a spin rate-lowering effect and thus improve the flight
performance. The hardnesses at specific positions of the core
interior are explained below.
[0026] The core surface hardness (Cs), expressed in terms of JIS-C
hardness, is preferably from 68 to 80, more preferably from 70 to
78, and even more preferably from 72 to 76. When the JIS-C hardness
value for the core surface hardness is too large, the feel at
impact may harden or the durability of the ball to cracking on
repeated impact may worsen. On the other hand, when this value is
too small, the spin rate may rise excessively and the rebound may
decrease, as a result of which the ball may not achieve a good
distance.
[0027] The core center hardness (Cc), expressed in terms of JIS-C
hardness, is preferably from 48 to 62, more preferably from 51 to
60, and even more preferably from 53 to 58. When the JIS-C hardness
value for the core center hardness is too large, the spin rate may
rise excessively, as a result of which a good distance may not be
obtained, and the ball may have a hard feel at impact. On the other
hand, when this value is too small, the durability to cracking on
repeated impact may worsen and the ball may have too soft a feel at
impact.
[0028] The JIS-C hardness at a position 5 mm from the core center
(C5) is preferably from 52 to 62, more preferably from 54 to 60,
and even more preferably from 56 to 68. The JIS-C hardness at a
position 10 mm from the core center (C10) is preferably from 56 to
67, more preferably from 58 to 65, and even more preferably from 60
to 63. When these hardness values are too large, the spin rate may
rise excessively, as a result of which a good distance may not be
obtained, and the ball may have a hard feel at impact. On the other
hand, when these values are too small, the durability to cracking
on repeated impact may worsen and the ball may have too soft a feel
at impact.
[0029] The JIS-C hardness at a position 15 mm from the core center
(C15) is preferably from 64 to 78, more preferably from 66 to 76,
and even more preferably from 68 to 74. When this hardness value is
too large, the ball may have a hard feel and the durability to
cracking on repeated impact may worsen. On the other hand, when
this hardness value is too small, the spin rate may rise
excessively and the rebound may decrease, as a result of which a
good distance may not be obtained.
[0030] The Cs-C15 value is preferably from 1 to 9, more preferably
from 2 to 7, and even more preferably from 3 to 5. 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 may rise excessively, as a result of which a good distance may
not be obtained.
[0031] The C15-C10 value is preferably from 4 to 15, more
preferably from 6 to 13, and even more preferably from 8 to 11.
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 may rise excessively, as a result of which
a good distance may not be obtained.
[0032] The C10-C5 value is preferably from 1 to 7, more preferably
from 2 to 5, and even more preferably from 3 to 4. When this value
falls outside of the above range, the spin rate on full shots may
rise excessively, as a result of which a good distance may not be
obtained. Also, the durability to cracking on repeated impact may
worsen.
[0033] The C5-Cc value is preferably from 0 to 7, more preferably
from 1 to 5, and even more preferably from 2 to 3. When this value
is too large, the spin rate may rise excessively, as a result of
which a good distance may not be obtained.
[0034] The C10-Cc value is preferably more than 0 and up to 10, and
more preferably from 2 to 8, meaning that the hardness gradient
from the core center (Cc) to a position 10 mm from the core center
(C10) is not very steep. When this value is too large, the spin
rate on full shots may rise excessively, as a result of which a
good distance may not be obtained.
[0035] The Cs-C10 value is preferably at least 10, and more
preferably from 11 to 15, meaning that the hardness gradient from a
position 10 mm from the core center (C10) out to the core surface
(Cs) is steep to a degree that exceeds a JIS-C hardness of 10. 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 excessively, as a result of
which a good distance may not be obtained.
[0036] It is critical for the Cs-C10 value to be larger than the
C10-Cc value, meaning that the hardness gradient is steeper in the
outer portion of the core than in the inner portion of the core.
That is, the value (Cs-C10)/(C10-Cc) is preferably from 1.0 to 5.0,
more preferably from 1.2 to 4.0, and even more preferably from 1.5
to 3.0. When this value is too large, the durability to cracking on
repeated impact may worsen. On the other hand, when this value is
too small, the spin rate may rise excessively, as a result of which
a good distance may not be obtained.
[0037] The hardness difference between the surface and center of
the core, i.e., the Cs-Cc value, is preferably from 15 to 30, more
preferably from 16 to 24, and even more preferably from 18 to 20.
When this hardness difference is too large, the durability to
cracking on repeated impact may worsen. On the other hand, when the
hardness difference is too small, the spin rate may rise
excessively, as a result of which a good distance may not be
obtained.
II. JIS-C Hardness Difference Between Core Surface and Center
.ltoreq.10
[0038] This core hardness profile is a profile that is nearly flat
with little gradient from the core surface to the core center. The
hardnesses at specific positions of the core interior are explained
below.
[0039] The core surface hardness (Cs), expressed in terms of JIS-C
hardness, is preferably from 59 to 73, more preferably from 61 to
71, and even more preferably from 63 to 69. When the JIS-C hardness
value for this core surface hardness is too large, the feel at
impact may harden or the durability of the ball to cracking on
repeated impact may worsen. On the other hand, when this value is
too small, the spin rate may rise excessively and the rebound may
decrease, as a result of which the ball may not achieve a good
distance.
[0040] The core center hardness (Cc), expressed in terms of JIS-C
hardness, is preferably from 56 to 68, more preferably from 58 to
66, and even more preferably from 60 to 64. When the JIS-C hardness
value for this core center hardness is too large, the spin rate may
rise excessively, as a result of which a good distance may not be
obtained, and the ball may have a hard feel at impact. On the other
hand, when this value is too small, the durability to cracking on
repeated impact may worsen and the ball may have too soft a feel at
impact.
[0041] The JIS-C hardness at a position 5 mm from the core center
(C5) is preferably from 56 to 68, more preferably from 58 to 66,
and even more preferably from 60 to 64. The JIS-C hardness at a
position 10 mm from the core center (C10) is preferably from 56 to
68, more preferably from 58 to 66, and even more preferably from 60
to 64. When these hardness values are too large, the spin rate may
rise excessively, as a result of which a good distance may not be
obtained, and the ball may have a hard feel at impact. On the other
hand, when these values are too small, the rebound may decrease, as
a result of which a good distance may not be obtained, and the feel
at impact may be too soft.
[0042] The JIS-C hardness at a position 15 mm from the core center
(C15) is preferably from 57 to 69, more preferably from 59 to 67,
and even more preferably from 61 to 65. When this hardness value is
too large, the ball may have a hard feel and the durability to
cracking on repeated impact may worsen. On the other hand, when
this hardness value is too small, the spin rate may rise
excessively and the rebound may decrease, as a result of which a
good distance may not be obtained.
[0043] The Cs-C15 value is preferably not more than 9, more
preferably from 0 to 7, and even more preferably from 1 to 5. 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 may rise, as a result of which a good distance may
not be obtained.
[0044] The C15-C10 value is preferably from 0 to .+-.3, more
preferably from 0 to .+-.2, and even more preferably from 0 to
.+-.1. When this value falls outside of this range, a good
durability to cracking on repeated impact may not be obtained.
[0045] The C10-C5 value is preferably from 0 to .+-.3, more
preferably from 0 to .+-.2, and even more preferably from 0 to
.+-.1. When this value falls outside of the above range, a good
durability to cracking on repeated impact may not be obtained.
[0046] The C5-Cc value is preferably from 0 to .+-.3, more
preferably from 0 to .+-.2, and even more preferably from 0 to
.+-.1. When this value falls outside of the above range, a good
durability to cracking on repeated impact may not be obtained.
[0047] The hardness difference between the core surface and the
core center, i.e., the Cs-C10 value, is preferably from 0 to 10,
more preferably from 1 to 8, and even more preferably from 2 to 6.
When this hardness difference value is too large, the durability to
cracking on repeated impact may worsen. On the other hand, when
this hardness difference value is too small, the spin rate on full
shots may rise excessively, as a result of which a good distance
may not be obtained.
[0048] The 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 at the spherical surface of
the core.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.).
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] Components A and B have already been described above.
[0058] 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.
[0059] 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.
[0060] It is also possible to add water directly to the rubber
composition. The following methods (i) to (iii) may be employed to
include water: [0061] (i) applying steam or ultrasonically applying
water in the form of a mist to some or all of the rubber
composition (compounded material); [0062] (ii) immersing some or
all of the rubber composition in water; [0063] (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.
[0064] 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.
[0065] 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 %.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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 3.2 to 4.6 mm, more preferably from 3.4
to 4.4 mm, and even more preferably from 3.6 to 4.2 mm. When this
value is too high, the feel of the ball may be too soft, the
durability to repeated impact may be poor, and 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.
[0072] 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. 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 falls outside of this range or is
thinner than the cover, the spin rate-reducing effects on shots
with a driver (W#1) may be inadequate, as a result of which a good
distance may not be achieved.
[0073] The intermediate layer material is not particularly limited,
although preferred use can be made of various thermoplastic resin
materials. To fully achieve 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.
[0074] By way of illustration, preferred use can be made of, as the
intermediate layer material, a material containing as the essential
component a base resin of, mixed in specific amounts: (a) an
olefin-unsaturated carboxylic acid random copolymer and/or a metal
ion neutralization product of an olefin-unsaturated carboxylic acid
random copolymer, and (b) an olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester random terpolymer and/or a
metal ion neutralization product of an olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester random
terpolymer.
[0075] Commercially available products may be used as components
(a) and (b). Illustrative examples of the random copolymer in
component (a) include Nucrel.RTM. N1560, N1214, N1035 and AN4221C
(all products of DuPont-Mitsui Polychemicals Co., Ltd.).
Illustrative examples of the random copolymer in component (b)
include Nucrel.RTM. AN4311, AN4318 and AN4319 (all products of
DuPont-Mitsui Polychemicals Co., Ltd.).
[0076] Illustrative examples of the metal ion neutralization
product of the random copolymer in component (a) include
Himilan.RTM. 1554, 1557, 1601, 1605, 1706 and AM7311 (all products
of DuPont-Mitsui Polychemicals Co., Ltd.), and Surlyn.RTM. 7930
(E.I. DuPont de Nemours & Co.). Illustrative examples of the
metal ion neutralization product of the random copolymer in
component (b) include Himilan.RTM. 1855, 1856 and AM7316 (all
products of DuPont-Mitsui Polychemicals Co., Ltd.), and Surlyn.RTM.
6320, 8320, 9320 and 8120 (all products of E.I. DuPont de Nemours
& Co.). Sodium-neutralized ionomer resins that are suitable as
the metal ion neutralization product of the random copolymer
include Himilan.RTM. 1605, 1601 and 1555.
[0077] When preparing the base resin, the weight ratio in which
component (a) and component (b) are mixed is set to generally
between 100:0 and 0:100. The ratio of component (a) with respect to
the combined amount of components (a) and (b) may be set to
preferably at least 50% by weight, more preferably at least 75% by
weight, and most preferably 100% by weight.
[0078] A non-ionomeric thermoplastic elastomer (e) may be added to
the base resin in order to enhance even further the feel of the
ball at impact and the ball rebound. Examples of component (e)
include olefin elastomers, styrene elastomers, polyester
elastomers, urethane elastomers and polyamide elastomers. To
further increase the rebound, it is preferable to use a polyester
elastomer or an olefin elastomer in this invention. The use of an
olefin elastomer consisting of a thermoplastic block copolymer
which includes crystalline polyethylene blocks as the hard segments
is especially preferred.
[0079] A commercially available product may be used as component
(e). Illustrative examples include Dynaron (JSR Corporation) and
the polyester elastomer Hytrel.RTM. (DuPont-Toray Co., Ltd.).
[0080] The content of component (e) must be set to more than 0
parts by weight. The upper limit may be set to preferably not more
than 100 parts by weight, more preferably not more than 60 parts by
weight, even more preferably not more than 50 parts by weight, and
most preferably not more than 40 parts by weight, per 100 parts by
weight of the base resin. When the component (e) content is too
high, the compatibility of the mixture may decrease and the
durability of the golf ball may markedly decline.
[0081] A fatty acid or fatty acid derivative having a molecular
weight of at least 228 and not more than 1,500 may be added to the
base resin as component (c). Compared with the base resin, this
component (c) has a very low molecular weight and, by suitably
adjusting the melt viscosity of the mixture, helps in particular to
improve the flow properties. Component (c) includes a relatively
high content of acid groups (or derivatives thereof), and can
suppress an excessive loss of resilience.
[0082] The amount of component (c) included per 100 parts by weight
of the resin component suitably composed of components (a), (b) and
(e) may be set to at least 5 parts by weight, preferably at least
10 parts by weight, more preferably at least 15 parts by weight,
and even more preferably at least 18 parts by weight. The upper
limit in the amount of component (c) may be set to not more than 80
parts by weight, preferably not more than 70 parts by weight, more
preferably not more than 60 parts by weight, and even more
preferably not more than 50 parts by weight. When the amount of
component (c) included is too small, the melt viscosity may
decrease, lowering the processability; when the amount included is
too large, the durability may decrease.
[0083] A basic inorganic metal compound capable of neutralizing
acid groups in the base resin and component (c) may be added as
component (d). By including component (d), the acid groups present
in the base resin and component (c) are neutralized and, owing to
synergistic effects from blending these components, the thermal
stability of the resin composition increases. At the same time, a
good moldability is imparted, enabling the resilience of the molded
product to be enhanced.
[0084] The amount of component (d) included per 100 parts by weight
of the above resin component must be at least 0.1 part by weight,
and may be set to preferably at least 0.5 part by weight, more
preferably at least 1 part by weight, and even more preferably at
least 2 parts by weight. The upper limit may be set to not more
than 17 parts by weight, preferably not more than 15 parts by
weight, more preferably not more than 13 parts by weight, and even
more preferably not more than 10 parts by weight. Including too
little component (d) fails to improve thermal stability and
resilience, whereas including too much lowers the heat resistance
of the golf ball material owing to the presence of excess basic
inorganic metal compound.
[0085] As mentioned above, by including specific amounts of
components (c) and (d) with respect to the resin component composed
of a base resin of specific amounts of components (a) and (b) in
admixture with optional component (e), the resin material can be
endowed with an excellent thermal stability, flowability and
moldability, and the resulting molded product can be endowed with a
dramatically improved resilience.
[0086] It is recommended that the material formulated from the
resin component and components (c) and (d) have a high degree of
neutralization (i.e., that it be highly neutralized). Specifically,
it is recommended that at least 50 mol %, preferably at least 60
mol %, more preferably at least 70 mol %, and even more preferably
at least 80 mol %, of the acid groups within the material be
neutralized. Such high neutralization of acid groups in the
material makes it possible to more reliably suppress the exchange
reactions that cause trouble when only a base resin and a fatty
acid (or fatty acid derivative) are used as in the above-cited
prior art, thus preventing the generation of fatty acid. As a
result, the thermal stability is greatly improved and the
moldability is good, enabling molded products to be obtained which
have an excellent resilience compared with prior-art ionomer
resins.
[0087] Here, "degree of neutralization" refers to the degree of
neutralization of acid groups present within the mixture of the
base resin and the fatty acid (or fatty acid derivative) serving as
component (c), and differs from the degree of neutralization of the
ionomer resin itself when an ionomer resin is used as the metal ion
neutralization product of a random copolymer in the base resin. On
comparing such a mixture having a certain degree of neutralization
with an ionomer resin alone having the same degree of
neutralization, the mixture of the invention, by including
component (d), contains a very large number of metal ions and thus
has a higher density of ionic crosslinks which contribute to
improved resilience, making it possible to confer the molded
product with an excellent resilience.
[0088] 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 amount thereof, per
100 parts by weight of components (a) to (e) 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.
[0089] It is advantageous to abrade the surface of the intermediate
layer in order to increase adhesion of the intermediate layer
material with the polyurethane that is preferably used in the
subsequently described cover (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.
[0090] 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.
[0091] Next, the cover, which is the outermost layer of the ball,
is described.
[0092] 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.
[0093] 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 shots
with a driver (W#1) and on iron shots may become too high, as a
result of which a good distance may not be obtained. When the
surface hardness is higher than this range, the spin rate on
approach shots may be inadequate or the feel at impact may be too
hard.
[0094] 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 3.2 to 4.1
mm, more preferably from 3.3 to 3.9 mm, and even more preferably
from 3.4 to 3.7 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.
[0095] 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.
[0096] 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.
[0097] 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.
[0098] The thermoplastic polyurethane (O) has a structure which
includes soft segments consisting of a polymeric polyol (polymeric
glycol) that is a long-chain polyol, and hard segments consisting
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.
[0099] 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. Examples of the chain extender
include, but are not limited to, 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.
[0100] 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.
[0101] 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.).
[0102] 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.
[0103] 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.
[0104] 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.
[0105] 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.
[0106] The golf ball of the invention preferably satisfies the
following conditions.
(1) Relationship Between Deflections Under Specific Loading of Core
and Ball
[0107] The relationship between the deflections of the core and the
ball under specific loading is optimized within a specific range.
That is, letting A 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 C 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 A-C 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
[0108] 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.
[0109] Also, the sum of the intermediate layer thickness and the
cover thickness is preferably from 1.6 to 3.0 mm, more preferably
from 1.8 to 2.8 mm, and even more preferably from 2.0 to 2.6 mm.
When this combined thickness is too large, the initial velocity may
decrease and the ball may not achieve a good distance on shots with
a driver (W#1). On the other hand, when this value is too small,
the durability on repeated impact may worsen.
(3) Relationship Between Surface Hardnesses of Ball and
Intermediate Layer-Encased Sphere
[0110] 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:
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
[0111] The relationship between the surface hardness of the core
and the surface hardness of 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 -22 to
0, more preferably from -18 to -5, and even more preferably from
-15 to -10. 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
[0112] Letting A 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 B 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 A-B is
preferably from 0.3 to 1.4, more preferably from 0.5 to 1.2, and
even more preferably from 0.6 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) Sum of Deflections of Core. Intermediate Layer-Encased Sphere
and Ball
[0113] Letting the deflection (mm) of the core, the intermediate
layer-encased sphere and the ball when compressed under a final
load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) be
respectively A, B and C, the sum A+B+C is at least 11.5 (with A
being at least 4.0 and C being at least 3.2), preferably from 11.5
to 13.0, more preferably from 11.7 to 12.8, and even more
preferably from 11.9 to 12.5. When this value is too large, the
durability to cracking on repeated impact may worsen and the
initial velocity 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 becomes too
high, as a result of which the intended distance is not obtained,
or the feel of the ball at impact becomes too hard.
(7) Relationship Between Surface Hardnesses of Intermediate
Layer-Encased Sphere and Core
[0114] The relationship between the surface hardness of the
intermediate layer-encased sphere and the surface hardness of 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 7 to 24,
more preferably from 10 to 20, and even more preferably from 13 to
16. 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.
(8) Relationship Between Initial Velocities of Intermediate
Layer-Encased Sphere and Core
[0115] The relationship between the initial velocity of the
intermediate layer-encased sphere and the initial velocity of the
core is optimized within a specific range. That is, the value
obtained by subtracting the initial velocity of the core from the
initial velocity of the intermediate layer-encased sphere is
preferably from 0 to 0.8 m/s, more preferably from 0.1 to 0.6 m/s,
and even more preferably from 0.2 to 0.4 m/s. When this value is
too large, the initial velocity of the finished ball may not
conform to the standard set by The Royal and Ancient Golf Club of
St. Andrews (R&A), which may make the ball unacceptable as an
official ball. On the other hand, when this value 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.
[0116] Also, the value obtained by dividing the initial velocity of
the intermediate layer-encased sphere by the initial velocity of
the core, or (initial velocity of intermediate layer-encased
sphere)/(initial velocity of core), must be at least 0.995, and is
preferably from 1.000 to 1.008, and more preferably from 1.004 to
1.006. When this value is too large, the initial velocity of the
finished ball may not conform to R&A standards, which may make
the ball unacceptable as an official ball. On the other hand, when
this value 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.
[0117] Here, in the relationship in (8) above, the initial velocity
of the core is preferably from 76.4 to 78.1 m/s, more preferably
from 76.8 to 77.9 m/s, and even more preferably from 77.2 to 77.5
m/s. The initial velocity of the intermediate layer-encased sphere
is preferably from 77.0 to 78.1 m/s, more preferably from 77.2 to
77.9 m/s, and even more preferably from 77.5 to 77.7 m/s. When
these values are too large, the initial velocity of the finished
ball may not conform to R&A standards, which may make the ball
unacceptable as an official ball. On the other hand, when this
value is too small, the finished ball has a low initial velocity
and the initial velocity of the ball on shots with a W#1 may be
low, as a result of which a good distance may not be achieved.
[0118] The initial velocity of the ball is typically at least 76.5
m/s, preferably at least 76.8 m/s, and more preferably from 77.0 to
77.7 m/s. At an initial velocity in excess of 77.724 m/s, the ball
does not conform to R&A standards, making it unacceptable as an
official ball. On the other hand, when this value is too small, the
initial velocity on shots with a driver (W#1) may decrease, as a
result of which a good distance may not be obtained. The initial
velocity of the ball in relation to the initial velocity of the
intermediate layer-encased sphere and the initial velocity of the
core preferably satisfies the following condition:
(initial velocity of ball)<(initial velocity of
core)<(initial velocity of intermediate layer-encased
sphere).
[0119] The initial velocities of the core, intermediate
layer-encased sphere and ball can 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.
In such a case, the core and intermediate layer-encased sphere can
be 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.
[0120] 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.
[0121] 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.
[0122] 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 Vo, defined as
the spatial volume of the individual dimples below the flat plane
circumscribed by the dimple edge, divided by the volume of the
cylinder whose base is the flat plane and whose height is the
maximum depth of the dimple from the base, to be set to at least
0.35 and 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.
[0123] 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
[0124] The following Examples and Comparative Examples are provided
to illustrate the invention, and are not intended to limit the
scope thereof.
Examples 1 to 5
Comparative Examples 1 to 6
Formation of Core
[0125] 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 3 4 5 1 2 3 4 5 6 Polybutadiene A 80 80 100 100
100 80 80 80 80 80 80 Polybutadiene B 20 20 20 20 20 20 20 20 Zinc
acrylate 27.5 26.5 28.0 27.5 27.4 33.5 36.5 27.5 27.5 27.5 26.5
Organic peroxide (1) 1.0 1.0 0.6 0.6 0.6 1.0 1.0 1.0 1.0 1.0 1.0
Organic peroxide (2) 0.6 0.6 0.6 Water 0.4 0.4 0.4 0.4 0.4 0.4 0.4
0.4 Antioxidant 0.1 0.1 0.2 0.2 0.2 0.1 0.1 0.1 0.1 0.1 0.1 Barium
sulfate 19.7 20.2 21.6 22.0 22.0 17.2 15.8 19.7 13.6 19.7 20.2 Zinc
oxide 4 4 5 5 5 4 4 4 4 4 4 Zinc salt of 0.5 0.5 1 1 1 0.5 0.5 0.5
0.5 0.5 0.5 pentachlorothiophenol Vulcanization First Temp. 155 155
145 145 145 155 155 155 155 155 155 conditions stage (.degree. C.)
Time 15 15 30 30 30 15 15 15 15 15 15 (min) Second Temp. -- -- 170
170 170 -- -- -- -- -- -- stage (.degree. C.) Time -- -- 10 10 7 --
-- -- -- -- -- (min)
[0126] Details on the ingredients shown in Table 1 are given below.
[0127] Polybutadiene A: Available under the trade name "BR 01" from
JSR Corporation [0128] Polybutadiene B: Available under the trade
name "BR 51" from JSR Corporation [0129] Zinc acrylate: Available
from Nippon Shokubai Co., Ltd. [0130] Organic peroxide (1): Dicumyl
peroxide, available under the trade name "Percumyl D" from NOF
Corporation [0131] 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 [0132] Water:
Distilled water, from Wako Pure Chemical Industries, Ltd. [0133]
Antioxidant: 2,2'-Methylenebis(4-methyl-6-butylphenol), available
under the trade name "Nocrac NS-6" from Ouchi Shinko Chemical
Industry Co., Ltd. [0134] Barium sulfate: Available under the trade
name "Barico #300" from Hakusui Tech [0135] Zinc oxide: Available
under the trade name "Zinc Oxide Grade 3" from Sakai Chemical Co.,
Ltd.
Formation of Intermediate Layer and Cover
[0136] 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 IV T-8295 75
100 T-8290 25 Himilan .RTM. 1706 37.5 Himilan .RTM. 1557 37.5
AN4319 20 25 AN4221C 80 Hytrel .RTM. 4001 11 11 Titanium oxide 3.9
3.9 2.0 Polyethylene wax 1.2 1.2 Isocyanate compound 7.5 7.5
Magnesium stearate 60 Calcium hydroxide 1.5 Magnesium oxide 1
Polytail H 8
[0137] Details on the materials shown in Table 2 are as follows.
[0138] T-8295, T-8290: MDI-PTMG type thermoplastic polyurethanes
available from DIC Bayer Polymer under the trademark Pandex. [0139]
Himilan.RTM. 1706, Himilan.RTM. 1557: [0140] Ionomers available
from DuPont-Mitsui Polychemicals Co., Ltd. [0141] AN4319, AN4221C:
An unneutralized ethylene-methacrylic acid-acrylic acid ester
terpolymer and an unneutralized ethylene-acrylic acid copolymer
(Nucrel.RTM., from DuPont-Mitsui Polychemicals Co., Ltd.) [0142]
Hytrel 4001: A polyester elastomer available from DuPont-Toray Co.,
Ltd. [0143] Polyethylene wax: "Sanwax 161P" from Sanyo Chemical
Industries, Ltd. [0144] Isocyanate compound: 4,4'-Diphenylmethane
diisocyanate [0145] Magnesium stearate: "Magnesium Stearate G" from
NOF Corporation [0146] Calcium hydroxide: "Calcium Hydroxide CLS-B"
from Shiraishi Calcium Kaisha, Ltd. [0147] Magnesium oxide:
"Kyowamag MF 150" from Kyowa Chemical Industry Co., Ltd. [0148]
Polytail H: Available from Mitsubishi Chemical Corporation
[0149] For each of the resulting golf balls, properties such as the
core hardness profile, thicknesses and material hardnesses of the
respective layers, and the surface hardnesses of various
layer-encased spheres were evaluated by the methods described
below. The results are shown in Table 3 (Working Examples) and
Table 4 (Comparative Examples).
Core Hardness Profile
[0150] 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.
[0151] 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.
[0152] The Shore D hardness at the core surface was measured with a
type D durometer in accordance with ASTM D2240-95.
Diameter of Core or Intermediate Layer-Encased Sphere
[0153] 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
[0154] 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
[0155] 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, differences between the
deflections (the A-B value and the A-C value) and the sum of the
deflections (the A+B+C value) were calculated.
Initial Velocities of Core, Intermediate Layer-Encased Sphere and
Ball
[0156] The initial velocities were 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 cores, intermediate layer-encased spheres and balls (referred
to below as "spherical test specimens") were held isothermally in a
23.9.+-.1.degree. C. environment for at least 3 hours, and then
tested in a chamber at a room temperature of 23.9.+-.2.degree. C.
Each spherical test specimen was hit using a 250-pound (113.4 kg)
head (striking mass) at an impact velocity of 143.8 ft/s (43.83
m/s). One dozen spherical test specimens were each hit four times.
The time taken for the test specimen to traverse a distance of 6.28
ft (1.91 m) was measured and used to compute the initial velocity
(m/s). This cycle was carried out over a period of about 15
minutes.
Material Hardnesses of Intermediate Layer and Cover (Shore D
Hardnesses)
[0157] 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 and Ball (Shore D
Hardnesses)
[0158] 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 1 2 3 4 5 Construction 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 32.9 32.9 32.9 Specific gravity
1.173 1.173 1.173 1.173 1.173 Deflection A (mm) 4.60 4.79 4.60 4.75
4.78 Hardness Surface hardness (Cs) 74 73 68 65 63 profile (JIS-C)
Hardness at position 71 70 64 62 62 15 mm from center (C15)
Hardness at position 61 61 63 61 61 10 mm from center (C10)
Hardness at position 58 57 63 61 61 5 mm from center (C5) Center
hardness (Cc) 55 54 63 61 61 Cs - C15 4 3 4 3 1 C15 - C10 9 9 1 1 1
C10 - C5 3 4 0 0 0 C5 - Cc 3 3 0 0 0 Surface - Center (Cs - Cc) 19
19 5 4 2 C10 - Cc 6 7 0 0 0 Cs - C10 13 12 5 4 2 (Cs - C10)/(C10 -
Cc) 2.3 1.7 -- -- -- Surface hardness (Shore D) 48 47 44 41 40
Initial velocity (m/s) 77.3 77.3 77.4 77.4 77.4 Intermediate
Material I I I I I layer Thickness (mm) 1.65 1.65 1.65 1.65 1.65
Specific gravity 0.96 0.96 0.96 0.96 0.96 Material hardness (Shore
D) 55 55 55 55 55 Intermediate Diameter (mm) 41.0 41.0 41.0 41.0
41.0 layer- Weight (g) 40.6 40.6 40.6 40.6 40.6 encased Deflection
B (mm) 3.93 4.08 3.90 4.07 4.10 sphere Surface hardness (Shore D)
63 63 63 63 63 Initial velocity (m/s) 77.6 77.6 77.7 77.7 77.7
Intermediate layer surface hardness - 15 16 19 22 23 Core surface
hardness Deflection difference (A - B) 0.67 0.71 0.70 0.68 0.68
Cover Material II II II II II Thickness (mm) 0.85 0.85 0.85 0.85
0.85 Specific gravity 1.15 1.15 1.15 1.15 1.15 Material hardness
(Shore D) 53 53 53 53 53 Ball Diameter (mm) 42.7 42.7 42.7 42.7
42.7 Weight (g) 45.5 45.5 45.5 45.5 45.5 Deflection C (mm) 3.50
3.59 3.48 3.57 3.59 Surface hardness (Shore D) 61 61 61 61 61
Initial velocity (m/s) 77.1 77.0 77.1 77.0 77.0 Core surface
hardness - -13 -14 -17 -20 -21 Ball surface hardness (Shore D) Ball
surface hardness - Intermediate -2 -2 -2 -2 -2 layer surface
hardness (Shore D) Intermediate layer thickness - 0.80 0.80 0.80
0.80 0.80 Cover thickness (mm) Deflection difference (A - C) 1.10
1.20 1.12 1.18 1.19 Sum of deflections (A + B + C) 12.02 12.46
11.98 12.39 12.47 Initial velocity of intermediate layer- 1.004
1.005 1.004 1.004 1.004 encased sphere/Core initial velocity
Initial velocity of intermediate layer- 0.31 0.38 0.32 0.32 0.32
encased sphere - Core initial velocity (m/s) Cover thickness +
Intermediate layer 2.50 2.50 2.50 2.50 2.50 thickness (mm)
TABLE-US-00004 TABLE 4 Comparative Example 1 2 3 4 5 6 Construction
3-piece 3-piece 3-piece 3-piece 3-piece 3-piece Core Diameter (mm)
37.7 37.7 37.7 39.5 37.7 37.7 Weight (g) 32.9 32.9 32.9 36.8 32.9
32.9 Specific gravity 1.173 1.173 1.173 1.140 1.173 1.173
Deflection A (mm) 3.49 2.95 4.60 4.60 4.60 4.79 Hardness Surface
hardness (Cs) 83 87 74 74 74 73 profile (JIS-C) Hardness at
position 77 81 71 71 71 70 15 mm from center (C15) Hardness at
position 65 68 61 61 61 61 10 mm from center (C10) Hardness at
position 64 68 58 58 58 57 5 mm from center (C5) Center hardness
(Cc) 61 62 58 58 58 54 Cs - C15 6 6 4 4 4 3 C15 - C10 12 14 9 9 9 9
C10 - C5 1 0 3 3 3 4 C5 - Cc 3 6 3 3 3 3 Surface - Center (Cs - Cc)
22 25 19 19 19 19 C10 - Cc 4 5 6 6 6 7 Cs - C10 18 19 13 13 13 12
(Cs - C10)/(C10 - Cc) 4.9 3.6 2.3 2.3 2.3 1.7 Surface hardness
(Shore D) 55 58 48 48 48 47 Initial velocity (m/s) 77.7 77.7 77.3
77.2 77.3 77.3 Intermediate Material I I I I IV IV layer Thickness
(mm) 1.65 1.65 1.65 0.75 1.65 1.65 Specific gravity 0.96 0.96 0.96
0.96 0.96 0.96 Material hardness (Shore D) 55 55 55 55 55 55
Intermediate Diameter (mm) 41.0 41.0 41.0 41.0 41.0 41.0 layer-
Weight (g) 40.6 40.6 40.6 40.6 40.6 40.6 encased Deflection B (mm)
3.02 2.58 3.93 4.13 3.91 4.06 sphere Surface hardness (Shore D) 63
63 63 63 63 63 Initial velocity (m/s) 77.7 77.8 77.6 77.6 76.7 76.6
Intermediate layer surface hardness - 8 5 15 15 15 16 Core surface
hardness Deflection difference (A - B) 0.46 0.37 0.67 0.47 0.69
0.73 Cover Material II II III II II II Thickness (mm) 0.85 0.85
0.85 0.85 0.85 0.85 Specific gravity 1.15 1.15 1.15 1.15 1.15 1.15
Material hardness (Shore D) 53 53 56 53 53 53 Ball Diameter (mm)
42.7 42.7 42.7 42.7 42.7 42.7 Weight (g) 45.5 45.5 45.5 45.5 45.5
45.5 Deflection C (mm) 2.75 2.35 3.40 3.57 3.48 3.57 Surface
hardness (Shore D) 61 61 64 61 61 61 Initial velocity (m/s) 77.1
77.1 77.0 77.0 76.4 76.3 Core surface hardness - -6 -3 -16 -13 -13
-14 Ball surface hardness (Shore D) Ball surface hardness -
Intermediate -2 -2 1 -2 -2 -2 layer surface hardness (Shore D)
Intermediate layer thickness - 0.80 0.80 0.80 -0.10 0.80 0.80 Cover
thickness (mm) Deflection difference (A - C) 0.73 0.60 1.20 1.03
1.12 1.22 Sum of deflections (A + B + C) 9.26 7.88 11.92 12.30
11.99 12.42 Initial velocity of intermediate layer- 1.001 1.001
1.004 1.005 0.992 0.992 encased sphere/Core initial velocity
Initial velocity of intermediate layer- 0.08 0.07 0.31 0.37 -0.64
-0.64 encased sphere - Core initial velocity (m/s) Cover thickness
+ Intermediate layer 2.50 2.50 2.50 1.60 2.50 2.50 thickness
(mm)
[0159] In addition, the flight performance (W#1), spin performance
on approach shots, feel 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 5.
Flight Performance (W#1 Shots)
[0160] A W#1 club (driver) was mounted on a golf swing robot, and
the distance traveled by the ball when struck at a head speed (HS)
of 35 m/s was measured and rated according to the criteria shown
below. The club was a PHYZ III driver (2011 model; loft angle,
11.5.degree.) manufactured by Bridgestone Sports Co., Ltd. The spin
rate was measured, using an apparatus for measuring the initial
conditions, immediately after the ball was similarly struck.
[0161] Rating Criteria: [0162] Good: Total distance was 152.0 m or
more [0163] Fair: Total distance was at least 151.0 m but less than
152.0 m [0164] NG: Total distance was less than 151.0 m
Spin Performance on Approach Shots
[0165] 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.
[0166] Rating Criteria: [0167] Good: Spin rate was 5,600 rpm or
more [0168] NG: Spin rate was less than 5,600 rpm
Feel
[0169] Sensory evaluations were carried out when the balls were hit
with a driver (W#1) by amateur golfers having head speeds of 30 to
40 m/s. The feel of the ball was rated according to the following
criteria.
[0170] Rating Criteria: [0171] Good: Six or more out of ten golfers
rated the feel as good [0172] Fair: Three to five out of ten
golfers rated the feel as good [0173] NG: Two or fewer out of ten
golfers rated the feel as good
[0174] Here, a "good feel" refers to a feel at impact that is
appropriately soft.
Durability to Cracking
[0175] The same type of driver (W#1) as that used 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
2, and the durability was rated according to the following
criteria.
Rating Criteria:
[0176] Excellent: Durability index was 110 or more [0177] Good:
Durability index was at least 95 but less than 110 [0178] NG:
Durability index was less than 95
TABLE-US-00005 [0178] TABLE 5 Example Comparative Example 1 2 3 4 5
1 2 3 4 5 6 Flight W#1 Spin rate 3,152 3,073 3,289 3,208 3,199
3,484 3,577 3,103 3,137 3,265 3,177 HS, 35 m/s (rpm) Total 153.5
154.0 151.2 151.7 151.5 149.7 148.5 153.8 152.3 148.0 148.3
distance (m) Rating good good fair fair fair NG NG good good NG NG
Performance Spin rate 5,654 5,618 5,659 5,622 5,607 5,817 5,852
5,506 5,595 5,659 5,623 on approach (rpm) shots Rating good good
good good good good good NG good good good Feel Rating good good
good good good fair NG good good good good Durability Rating good
good Exc. Exc. Exc. good good good NG good good to cracking
[0179] In Comparative Example 1, the ball deflection, intermediate
layer-encased sphere deflection and core deflection under specific
loading were all small, meaning that each of these spheres was
hard. As a result, the spin rate on full shots with a W#1 was high
and a good distance was not obtained. Also, the ball had a hard
feel at impact.
[0180] In Comparative Example 2, the ball deflection, intermediate
layer-encased sphere deflection and core deflection under specific
loading were all small, meaning that each of these spheres was
hard. As a result, the spin rate on full shots with a W#1 was high
and a good distance was not obtained. Also, the ball had a hard
feel at impact.
[0181] In Comparative Example 3, the surface hardness of the ball
was higher than the surface hardness of the intermediate
layer-encased sphere. As a result, the spin performance on approach
shots was poor.
[0182] In Comparative Example 4, the intermediate layer thickness
was smaller than the cover thickness. As a result, the spin rate on
full shots with a W#1 was high and a good distance was not
obtained. Also, the durability on repeated impact was poor.
[0183] In Comparative Example 5, the (initial velocity of
intermediate layer-encased sphere)/(core initial velocity) value
was smaller than 0.995, as a result of which the ball had a low
initial velocity. In addition, the spin rate on full shots rose and
so the intended distance was not achieved.
[0184] In Comparative Example 6, the (initial velocity of
intermediate layer-encased sphere)/(core initial velocity) value
was smaller than 0.995, as a result of which the ball had a low
initial velocity. In addition, the spin rate on full shots rose and
so the intended distance was not achieved.
[0185] Japanese Patent Application No. 2015-118026 is incorporated
herein by reference.
[0186] 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.
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