U.S. patent application number 12/757512 was filed with the patent office on 2011-10-13 for multi-piece solid golf ball.
This patent application is currently assigned to Bridgestone Sports Co., Ltd.. Invention is credited to Hiroshi Higuchi, Takuma Nakagawa, Katsunori Sato, Junji UMEZAWA.
Application Number | 20110250987 12/757512 |
Document ID | / |
Family ID | 44761335 |
Filed Date | 2011-10-13 |
United States Patent
Application |
20110250987 |
Kind Code |
A1 |
UMEZAWA; Junji ; et
al. |
October 13, 2011 |
MULTI-PIECE SOLID GOLF BALL
Abstract
The invention provides a multi-piece solid golf ball having a
solid core, an inner cover layer and an outer cover layer, which
outer cover layer has a plurality of dimples on a surface thereof.
The value obtained by subtracting a material hardness (Shore D) of
the outer cover layer from a material hardness (Shore D) of the
inner cover layer is greater than -5 and less than +5. The dimples
number at least 250 and not more than 500, have a surface coverage
(SR) of at least 70% and a volume ratio (VR) of at least 1.0%, are
of at least three types of mutually differing dimple diameter (DM)
and/or dimple depth (DP), and have an average depth of at least
about 0.18 mm and a diameter-to-depth ratio (DM/DP) of not more
than about 23. The ball has a coefficient of lift CL at a Reynolds
number of 70,000 and a spin rate of 2,000 rpm which is maintained
at 60% or more of the coefficient of lift CL at a Reynolds number
of 80,000 and a spin rate of 2,000. This multi-piece solid golf
ball is able to substantially reduce the distance traveled by the
ball when struck at a high HS, while at the same time holding down
the reduction in distance when struck at a low HS.
Inventors: |
UMEZAWA; Junji;
(Chichibu-shi, JP) ; Sato; Katsunori;
(Chichibu-shi, JP) ; Higuchi; Hiroshi;
(Chichibu-shi, JP) ; Nakagawa; Takuma;
(Chichibu-shi, JP) |
Assignee: |
Bridgestone Sports Co.,
Ltd.
Tokyo
JP
|
Family ID: |
44761335 |
Appl. No.: |
12/757512 |
Filed: |
April 9, 2010 |
Current U.S.
Class: |
473/374 ;
473/384 |
Current CPC
Class: |
A63B 37/0045 20130101;
A63B 37/002 20130101; A63B 37/0083 20130101; A63B 37/0031 20130101;
A63B 37/0033 20130101; A63B 37/008 20130101; A63B 37/0012 20130101;
A63B 37/0017 20130101; A63B 37/0066 20130101; A63B 37/0018
20130101; A63B 37/0021 20130101; A63B 37/0064 20130101; A63B
37/0065 20130101; A63B 37/0019 20130101; A63B 37/0096 20130101;
A63B 37/0043 20130101; A63B 37/009 20130101; A63B 37/0006 20130101;
A63B 37/0075 20130101; A63B 37/0092 20130101; A63B 37/0004
20130101; A63B 37/0077 20130101; A63B 37/0084 20130101 |
Class at
Publication: |
473/374 ;
473/384 |
International
Class: |
A63B 37/14 20060101
A63B037/14; A63B 37/04 20060101 A63B037/04 |
Claims
1. A multi-piece solid golf ball comprising a solid core, an inner
cover layer and an outer cover layer, which outer cover layer has a
plurality of dimples on a surface thereof, wherein a value obtained
by subtracting a material hardness (Shore D) of the outer cover
layer from a material hardness (Shore D) of the inner cover layer
is greater than -5 and less than +5; the dimples number at least
250 but not more than 500, have a surface coverage (SR) of at least
70% and a volume ratio (VR) of at least 1.0%, are of at least three
types of mutually differing dimple diameter (DM) and/or dimple
depth (DP), and have an average depth of at least about 0.18 mm and
a diameter-to-depth ratio (DM/DP) of not more than about 23; and
the ball has a coefficient of lift CL at a Reynolds number of
70,000 and a spin rate of 2,000 rpm which is maintained at 60% or
more of the coefficient of lift CL at a Reynolds number of 80,000
and a spin rate of 2,000.
2. The multi-piece solid golf ball of claim 1 wherein, letting Da
represent a dimple having a diameter of at least 3.7 mm and Db
represent a dimple having a diameter of less than 3.7 mm, the ratio
(total number of Db)/(total number of Da) is at least about 0.005
but not more than about 1.
3. The multi-piece solid golf ball of claim 2, wherein dimples Da
of at least 3.7 mm account for at least about 75% of the total
dimple volume.
4. The multi-piece solid golf ball of claim 1, wherein the material
hardness (Shore D) of the inner cover layer is from 45 to 65.
5. The multi-piece solid golf ball of claim 1, wherein the material
hardness (Shore D) of the outer cover layer is from 45 to 65.
6. The multi-piece solid golf ball of claim 1, wherein the value
obtained by subtracting the material hardness (Shore D) of the
outer cover layer from the material hardness (Shore D) of the inner
cover layer is within .+-.4.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a multi-piece solid golf
ball having a solid core, an inner cover layer and an outer cover
layer, and having a plurality of dimples on a surface of the outer
cover layer. More specifically, the invention relates to a
multi-piece solid golf ball which substantially reduces the
distance traveled by the ball when struck at a high head speed
(head speed is sometimes abbreviated below as "HS") while at the
same time undergoing little reduction in distance when struck at a
low HS.
[0002] With recent advances in golfing equipment such as balls and
clubs, golf balls have come to travel increasing distances. For
this reason, to keep play fair, strict rules have been adopted
which establish, in the case of a golf club, for example, the size
of the head and the length of the shaft. Similarly, limitations
have been placed on certain characteristics of the golf ball, such
as its size, weight and initial velocity, so as to restrict
excessive ball travel of the sort that would result in a loss of
fair play.
[0003] The distance traveled by a golf ball is generally held down
by limiting the initial velocity. However, in such cases, both at
high head speeds and low head speeds, the distance traveled is
often reduced in about the same ratio. As a result, such balls have
significant drawbacks for low HS players.
[0004] As another approach, a variety of golf balls have been
disclosed which, by optimizing the dimples on the surface of the
ball, lower the flight trajectory and hold down decreases in
distance.
[0005] For example, JP-A 05-103846 describes a golf ball in which
the dimple diameter, dimple depth and number of dimples have been
optimized. JP-A 10-043342 and JP-A 10-043343 disclose golf balls in
which the amount of deformation by a ball when compressed under a
load of 100 kgf has been optimized, along with which the dimple
diameter divided by the dimple depth has been set to from 10 to 15
or the dimple space volume as a proportion of the total volume of a
hypothetical sphere were the surface of the ball to have no dimples
thereon has been set to from 0.7 to 1.1%. JP-A 2000-107338
discloses a practice golf ball in which the ball weight and
diameter have been optimized.
[0006] In addition, JP-A 11-47311 and JP-A 11-47312 disclose solid
golf balls in which an inner cover layer and an outer cover layer
have the same or substantially similar Shore D hardnesses.
[0007] It is therefore an object of the present invention to
provide a golf ball which can achieve a superior distance in a low
HS range while holding down the distance traveled in a high HS
range.
SUMMARY OF THE INVENTION
[0008] The inventors have conducted extensive investigations in
order to achieve the above object. As a result, they have found
that, in a multi-piece solid golf ball composed of a solid core, an
inner cover layer and an outer cover layer, which outer cover layer
has a plurality of dimples on a surface thereof, by specifying the
size relationship between the material hardnesses (Shore D) of the
inner cover layer and the outer cover layer; by specifying, for the
dimples formed on the surface of the outer cover layer, the number
of dimples, dimple surface coverage (SR), dimple volume ratio (VR),
dimple types, average dimple depth, and dimple diameter-to-depth
ratio (DM/DP); and by having the coefficient of lift CL at a
Reynolds number of 70,000 and a spin rate of 2,000 rpm maintained
at 60% or more of the coefficient of lift CL at a Reynolds number
of 80,000 and a spin rate of 2,000, synergistic effects arising
from dimple optimization and the suitable hardness relationship
between the inner cover layer and the outer cover layer make it
possible to substantially reduce the distance traveled by the ball
when struck at a high HS while at the same time holding down the
decrease in distance when the ball is struck at a low HS.
[0009] That is, unlike conventional methods of lowering the ball
initial velocity or core initial velocity, the golf ball of the
present invention is able, by combining low-trajectory dimples with
the interior structure (multilayer structure) of the ball, to
substantially reduce the distance of the ball when struck at a high
HS while at the same time holding down to the extent possible,
relative to the reduction in distance at high HS, the reduction in
distance on low HS shots. As used herein, "distance" refers to the
total distance traveled by a golf ball, including both the carry
and the run.
[0010] Accordingly, the invention provides the following
multi-piece solid golf balls. [0011] [1] A multi-piece solid golf
ball comprising a solid core, an inner cover layer and an outer
cover layer, which outer cover layer has a plurality of dimples on
a surface thereof, wherein a value obtained by subtracting a
material hardness (Shore D) of the outer cover layer from a
material hardness (Shore D) of the inner cover layer is greater
than -5 and less than +5; the dimples number at least 250 and not
more than 500, have a surface coverage (SR) of at least 70% and a
volume ratio (VR) of at least 1.0%, are of at least three types of
mutually differing dimple diameter (DM) and/or dimple depth (DP),
and have an average depth of at least about 0.18 mm and a
diameter-to-depth ratio (DM/DP) of not more than about 23; and the
ball has a coefficient of lift CL at a Reynolds number of 70,000
and a spin rate of 2,000 rpm which is maintained at 60% or more of
the coefficient of lift CL at a Reynolds number of 80,000 and a
spin rate of 2,000. [0012] [2] The multi-piece solid golf ball of
[1] wherein, letting Da represent a dimple having a diameter of at
least 3.7 mm and Db represent a dimple having a diameter of less
than 3.7 mm, the ratio (total number of Db)/(total number of Da) is
at least about 0.005 but not more than about 1. [0013] [3] The
multi-piece solid golf ball of [2], wherein dimples Da of at least
3.7 mm account for at least about 75% of the total dimple volume.
[0014] [4] The multi-piece solid golf ball of [1], wherein the
material hardness (Shore D) of the inner cover layer is from 45 to
65. [0015] [5] The multi-piece solid golf ball of [1], wherein the
material hardness (Shore D) of the outer cover layer is from 45 to
65. [0016] [6] The multi-piece solid golf ball of [1], wherein the
value obtained by subtracting the material hardness (Shore D) of
the outer cover layer from the material hardness (Shore D) of the
inner cover layer is within .+-.4.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0017] FIG. 1 is a cross-sectional view showing the internal
structure of a multi-piece solid golf ball according to an
embodiment of the present invention.
[0018] FIG. 2 is a schematic view illustrating a dimple used in the
present invention.
[0019] FIG. 3 is a top view of a golf ball showing a dimple pattern
(I) used on a ball in an example of the invention.
[0020] FIG. 4 is a top view of a golf ball showing a dimple pattern
(II) used on a ball in an example of the invention.
[0021] FIG. 5 is a front view of a golf ball showing a dimple
pattern (III) used on a ball in a comparative example.
[0022] FIG. 6 is a front view of a golf ball showing a dimple
pattern (IV) used on a ball in a comparative example.
[0023] FIG. 7 is a front view of a golf ball showing a dimple
pattern (V) used on a ball in a comparative example.
[0024] FIG. 8 is a front view of a golf ball showing a dimple
pattern (VI) used on a ball in a comparative example.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The invention is described more fully below.
[0026] The golf ball of the invention is a multi-piece solid golf
ball having a solid core (referred to below as simply the "core"),
an inner cover layer and an outer cover layer. The outer cover
layer has a surface with a plurality of dimples formed thereon. By
combining an inner cover layer and an outer cover layer having a
specific relationship between the material hardnesses thereof with
dimples which satisfy the subsequently described specific
parameters, the distance traveled by the ball on shots at a high HS
can be substantially reduced while suppressing a decrease in the
distance traveled by the ball on shots at a low HS. As used in the
present invention, "high HS range" refers to a range of about 50 to
60 m/s and "low HS range" refers to a range of 30 to 40 m/s.
[0027] Regarding the interior structure of the golf ball G of the
present invention, as shown in FIG. 1, the ball G has a three-layer
construction composed of at least a core 1, an inner cover layer 2
encasing the core 1, and an outer cover layer 3 encasing the inner
cover layer 2. In this invention, the inner cover layer 2 and the
outer cover layer 3 are sometimes referred to collectively as the
"cover." A plurality of dimples D are generally formed on the
surface of the outer cover layer 3, and these dimples D satisfy the
specific parameters of the invention. It should be noted that,
although FIG. 1 shows a three-layer construction arrived at by
forming a core 1, an inner cover layer 2 and an outer cover layer
3, any of these layers may optionally be formed as a plurality of
two or more layers without departing from the scope of the
invention. For example, the core may be formed as a plurality of
layers.
[0028] The core in the invention may be formed using a rubber
composition containing, for example, a base rubber and also such
ingredients as a co-crosslinking agent, an organic peroxide, an
inert filler, sulfur and an organosulfur compound. The base rubber
of the rubber composition is preferably one composed primarily of a
known polybutadiene.
[0029] In the present invention, an organosulfur compound may be
optionally included in the base rubber in order to increase the
rebound of the core. When an organosulfur compound is included, the
amount included per 100 parts by weight of the base rubber may be
set to preferably at least 0.05 part by weight, more preferably at
least 0.1 part by weight, and even more preferably at least 0.2
part by weight. The upper limit in the amount included may be set
to preferably not more than 5 parts by weight, more preferably not
more than 4 parts by weight by weight, and even more preferably not
more than 2 parts by weight. If the amount of organosulfur compound
included is too small, a sufficient core rebound-increasing effect
may not be obtained. On the other hand, if too much organosulfur
compound is included, the core may become too soft, resulting in a
poor feel when the ball is played and a poor durability to cracking
on repeated impact.
[0030] The diameter of the core, although not subject to any
particular limitation, may be set to from 30 to 40 mm. In this
case, the lower limit value is preferably at least 32 mm, more
preferably at least 34 mm, and even more preferably at least 35 mm.
The upper limit value may be set to preferably not more than 39.5
mm, more preferably not more than 39 mm, and even more preferably
not more than 38.5 mm.
[0031] The core deflection, meaning the amount of deflection when
compressed under a final load of 1,275 N (130 k.sub.gf) from an
initial load of 98 N (10 kgf), although not subject to any
particular limitation, may be set within a range of from 2.0 to 6.0
mm. In this case, the lower limit value is preferably at least 2.5
mm, more preferably at least 2.8 mm, and even more preferably at
least 3.2 mm. The upper limit value may be set to preferably not
more than 5.5 mm, more preferably not more than 5.0 mm, and even
more preferably not more than 4.5 mm. If the core is too much
harder than the above range (small deflection), the spin will rise
excessively, which is unsuitable for the dimples of the present
invention. On the other hand, if the core is too much softer than
the above range (large deflection), the feel of the ball may become
too soft and the durability to cracking on repeated impact may
worsen.
[0032] The specific gravity of the core, while not subject to any
particular limitation, may be set within a range of from 0.9 to
1.4. In such a case, the lower limit value is preferably at least
1.0, and more preferably at least 1.1. The upper limit value may be
set to preferably not more than 1.3, and more preferably not more
than 1.2.
[0033] In the present invention, by using the above material to
form the solid core 1, the rebound can be increased, thus enabling
a golf ball capable of achieving a stable trajectory to be
provided.
[0034] In the golf ball G of the invention, an inner cover layer 2
and an outer cover layer 3 are formed around the above solid core
1. In this invention, it is critical for the difference between the
material hardness (Shore D) of the inner cover layer and the
material hardness (Shore D) of the outer cover layer to be adjusted
so as to be small. Specifically, the value obtained by subtracting
the material hardness (Shore D) of the outer cover layer from the
material hardness (Shore D) of the inner cover layer must be
greater than -5 and less than +5. It is recommended that this value
be more preferably within .+-.4, even more preferably within .+-.3,
and most preferably within .+-.2. When the above hardness
difference is too large, the feel on impact may not be good. Here,
"material hardness (Shore D)" refers to the hardness of a sheet of
the cover material that has been formed under applied pressure to a
thickness of about 2 mm, as measured using a type D durometer in
general accordance with ASTM D2240. This is referred to below as
the "Shore D hardness."
[0035] The respective Shore D hardnesses and thicknesses of the
inner cover layer and the outer cover layer are not subject to any
particular limitation, although it is recommended that these values
be set as follows in the present invention.
[0036] First of all, the Shore D hardness of the inner cover layer,
although not subject to any particular limitation, may be set to at
least 45, preferably at least 48, more preferably at least 51, and
most preferably at least 55. It is recommended that the upper limit
be not more than 65, preferably not more than 63, more preferably
not more than 61, and most preferably not more than 60. When the
Shore D hardness of the inner cover layer is too high, the ball may
have a poor feel on impact.
[0037] The thickness of the inner cover layer, although not subject
to any particular limitation, may be set to at least 0.5 mm,
preferably at least 0.7 mm, more preferably at least 1.0 mm, and
still more preferably at least 1.3 mm. It is recommended that the
upper limit be not more than 3.0 mm, preferably not more than 2.5
mm, even more preferably not more than 2.3 mm, and most preferably
not more than 2.2 mm. When the inner cover layer is too thin, the
durability may worsen; when it is too thick, the ball may have a
poor feel on impact.
[0038] The Shore D hardness of the outer cover layer, although not
subject to any particular limitation, may be set to at least 45,
preferably at least 48, more preferably at least 51, and most
preferably at least 54. It is recommended that the upper limit be
not more than 65, preferably not more than 63, more preferably not
more than 61, and most preferably not more than 60. If the Shore D
hardness of the outer cover layer is too low, the feel on impact
may be too soft. On the other hand, if it is too high, the
durability or the feel on impact may worsen.
[0039] The thickness of the outer cover layer, although not subject
to any particular limitation, may be set to at least 0.5 mm,
preferably at least 0.7 mm, and more preferably at least 0.8 mm. It
is recommended that the upper limit be not more than 3.0 mm,
preferably not more than 2.5 mm, more preferably not more than 2.0
mm, and even preferably not more than 1.6 mm. If the thickness of
the outer cover layer falls outside the above range, this may lead
to a worsening in the feel of the ball on impact or in the
durability.
[0040] The cover having the above construction may be formed of a
known material exemplified by thermoplastic resins such as
ionomeric resins, and various types of thermoplastic elastomers.
Examples of thermoplastic elastomers include polyester-based
thermoplastic elastomers, polyamide-based thermoplastic elastomers,
polyurethane-based thermoplastic elastomers, olefin-based
thermoplastic elastomers and styrene-based thermoplastic
elastomers.
[0041] In the present invention, such cover materials are not
subject to any particular limitation, although preferred use may be
made of a cover material composed primarily of a material selected
from the group consisting of the polyurethane materials (I),
polyurethane materials (II) and ionomeric resin materials shown
below. These materials, including molding methods, are described in
order below.
Polyurethane Material (I)
[0042] This material (I) is composed primarily of components A and
B below: [0043] (A) a thermoplastic polyurethane material, [0044]
(B) an isocyanate mixture obtained by dispersing (B-1) an
isocyanate compound having as functional groups at least two
isocyanate groups per molecule in (B-2) a thermoplastic resin that
is substantially non-reactive with isocyanate.
[0045] Golf balls in which the cover has been formed of this
material (I) can be endowed with an excellent feel,
controllability, cut resistance, scuff resistance and durability to
cracking on repeated impact.
[0046] Next, each of the above components is described.
[0047] The thermoplastic polyurethane material (A) has a structure
which includes soft segments made of a polymeric polyol (polymeric
glycol), and hard segments made of a chain extender and a
diisocyanate. Here, the polymeric polyol used as a starting
material is not subject to any particular limitation, and may be
any that is used in the prior art relating to thermoplastic
polyurethane materials, such as polyester polyols and polyether
polyols. Polyether polyols are preferable to polyester polyols
because they enable the synthesis of thermoplastic polyurethane
materials having a high rebound resilience and excellent
low-temperature properties. Illustrative examples of polyether
polyols include polytetramethylene glycol and polypropylene glycol.
Polytetramethylene glycol is especially preferred from the
standpoint of the rebound resilience and low-temperature
properties. The polymeric polyol has an average molecular weight of
preferably from 1,000 to 5,000. A molecular weight of from 2,000 to
4,000 is especially preferred for synthesizing thermoplastic
polyurethane materials having a high rebound resilience.
[0048] The chain extender employed is preferably one which is used
in the art relating to conventional thermoplastic polyurethane
materials. Illustrative, non-limiting, examples include
1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol,
1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. These chain
extenders have an average molecular weight of preferably from 20 to
15,000.
[0049] The diisocyanate employed is preferably one which is used in
the art relating to conventional thermoplastic polyurethane
materials. Illustrative, non-limiting, examples include aromatic
diisocyanates such as 4,4'-diphenylmethane diisocyanate,
2,4-toluene diisocyanate and 2,6-toluene diisocyanate; and
aliphatic diisocyanates such as hexamethylene 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, for stable reactivity with the
subsequently described isocyanate mixture (B), it is most
preferable to use the following aromatic diisocyanate:
4,4'-diphenylmethane diisocyanate.
[0050] A commercial product may be advantageously used as the
thermoplastic polyurethane material composed of the above-described
material. Illustrative examples include those available under the
trade names Pandex T-8290, Pandex T-8295 and Pandex T8260 (DIC
Bayer Polymer, Ltd.), and those available under the trade names
Resamine 2593 and Resamine 2597 (Dainichi Seika Colour &
Chemicals Mfg. Co., Ltd.).
[0051] The isocyanate mixture (B) is obtained by dispersing (B-1)
an isocyanate compound having as functional groups at least two
isocyanate groups per molecule in (B-2) a thermoplastic resin that
is substantially non-reactive with isocyanate. Here, the isocyanate
compound (B-1) is preferably an isocyanate compound used in the
prior art relating to thermoplastic polyurethane materials.
Illustrative, non-limiting, examples include aromatic diisocyanates
such as 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate
and 2,6-toluene diisocyanate; and aliphatic diisocyanates such as
hexamethylene diisocyanate. From the standpoint of reactivity and
work safety, the use of 4,4'-diphenylmethane diisocyanate is most
preferred.
[0052] The thermoplastic resin (B-2) is preferably a resin having a
low water absorption and excellent compatibility with thermoplastic
polyurethane materials. Illustrative examples of such resins
include polystyrene resins, polyvinyl chloride resins, ABS resins,
polycarbonate resins, and polyester elastomers (e.g.,
polyether-ester block copolymers, polyester-ester block
copolymers). From the standpoint of the rebound resilience and
strength, the use of a polyester elastomer, particularly a
polyether-ester block copolymer, is especially preferred.
[0053] In the isocyanate mixture (B), it is desirable for the
relative proportions of the thermoplastic resin (B-2) and the
isocyanate compound (B-1), expressed as the weight ratio
(B-2):(B-1), to be from 100:5 to 100:100, and especially from
100:10 to 100:40. If the amount of the isocyanate compound (B-1)
relative to the thermoplastic resin (B-2) is too small, a greater
amount of the isocyanate mixture (B) will have to be added to
achieve an amount of addition sufficient for the crosslinking
reaction with the thermoplastic polyurethane material (A). As a
result, the thermoplastic resin (B-2) will exert a large influence,
rendering the physical properties of the material inadequate. On
the other hand, if the amount of the isocyanate compound (B-1)
relative to the thermoplastic resin (B-2) is too large, the
isocyanate compound (B-1) may cause slippage to occur during
mixing, making preparation of the isocyanate mixture (B)
difficult.
[0054] The isocyanate mixture (B) may be obtained by, for example,
adding the isocyanate compound (B-1) to the thermoplastic resin
(B-2) and thoroughly working together these components at a
temperature of from 130 to 250.degree. C. using mixing rolls or a
Banbury mixer, then either pelletizing or cooling and subsequently
grinding. A commercial product such as that available under the
trade name Crossnate EM30 (Dainichi Seika Colour & Chemicals
Mfg. Co., Ltd.) may be suitably used as the isocyanate mixture
(B).
[0055] The above material (I) is composed primarily of the
thermoplastic polyurethane material (A) and isocyanate mixture (B)
described above. In this material (I), the isocyanate mixture (B)
is included in an amount, per 100 parts by weight of the
thermoplastic polyurethane material (A), of at least 1 part by
weight, preferably at least 5 parts by weight, and more preferably
at least 10 parts by weight, but not more than 100 parts by weight,
preferably not more than 50 parts by weight, and more preferably
not more than 30 parts by weight. If too little isocyanate mixture
(B) is included relative to the thermoplastic polyurethane material
(A), a sufficient crosslinking effect will not be achieved. On the
other hand, if too much is included, this may lead to discoloration
of the molded material by unreacted isocyanate, which is
undesirable.
[0056] In addition to above components (A) and (B), another
component (C), although not essential, may also be included in the
material (I). This other component is exemplified by thermoplastic
polymeric materials other than thermoplastic polyurethane
materials; illustrative examples include polyester elastomers,
polyamide elastomers, ionomeric resins, styrene block elastomers,
polyethylene, and nylon resins. When component (C) is included, the
amount is not subject to any particular limitation and may be
suitably selected as appropriate for such purposes as adjusting the
hardness, improving the resilience, improving the flow properties,
and improving the adhesion of the cover material. The amount of
component (C) included per 100 parts by weight of component (A) is
set to preferably at least 10 parts by weight, and the upper limit
is set to not more than 100 parts by weight, preferably not more
than 75 parts by weight, and more preferably not more than 50 parts
by weight. If necessary, various additives such as pigments,
dispersants, antioxidants, light stabilizers, ultraviolet absorbers
and parting agents may also be suitably included in the above
material (I).
[0057] Formation of the cover using the above material (I) may be
carried out by a known molding method. For example, the cover may
be molded by adding the isocyanate mixture (B) to the thermoplastic
polyurethane material (A) and dry mixing, feeding the resulting
mixture to an injection molding machine, and injecting the molten
resin blend over the core. In such a case, the molding temperature
varies with the type of thermoplastic polyurethane material (A),
although molding is generally carried out within a temperature
range of 150 to 250.degree. C.
[0058] Reactions and crosslinking which take place in the golf ball
cover obtained as described above are believed to involve the
reaction of isocyanate groups with hydroxyl groups remaining in the
thermoplastic polyurethane material to form urethane bonds, or the
creation of an allophanate or biuret crosslinked form via a
reaction involving the addition of isocyanate groups to urethane
groups in the thermoplastic polyurethane material. Although the
crosslinking reaction has not yet proceeded to a sufficient degree
immediately after injection molding of the material (I), the
crosslinking reaction can be made to proceed further by carrying
out an annealing step after molding, in this way conferring the
golf ball cover with useful characteristics. "Annealing," as used
herein, refers to heat aging the cover at a constant temperature
for a fixed length of time, or aging the cover for a fixed period
at room temperature.
Polyurethane Material (II)
[0059] This material (II) is a single resin blend in which the
primary components are (D) a thermoplastic polyurethane and (E) a
polyisocyanate compound. By forming a cover composed primarily of
such a polyurethane material (II), it is possible to achieve an
excellent feel, controllability, cut resistance, scuff resistance
and durability to cracking on repeated impact without a loss of
resilience.
[0060] As used herein, reference to a "single" resin blend means
that the resin blend is not fed as a plurality of types of pellets,
but rather is supplied to, for example, an injection molding
machine as one type of pellet prepared by incorporating a plurality
of ingredients into individual pellets.
[0061] To fully and effectively achieve the objects of the
invention, a necessary and sufficient amount of unreacted
isocyanate groups should be present within the cover resin
material. Specifically, it is recommended that the combined weight
of above components (D) and (E) account for at least 60%, and
preferably at least 70%, of the total weight of the cover.
Components (D) and (E) are described in detail below.
[0062] The above thermoplastic polyurethane (D) is described. The
thermoplastic polyurethane structure includes soft segments made of
a polymeric polyol (polymeric glycol) that is a long-chain polyol,
and hard segments made of a chain extender and a polyisocyanate
compound. Here, the long-chain polyol used as a starting material
is not subject to any particular limitation, and may be any that
has hitherto been used in the art relating to thermoplastic
polyurethanes. Exemplary long-chain polyols 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 as combinations of two or more thereof. Of
the long-chain polyols mentioned here, polyether polyols are
preferred because they enable the synthesis of thermoplastic
polyurethanes having a high rebound resilience and excellent
low-temperature properties.
[0063] Illustrative examples of the above polyether polyol include
poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene
glycol) and poly(methyltetramethylene glycol) obtained by the
ring-opening polymerization of cyclic ethers. These polyether
polyols may be used singly or as a combination of two or more
thereof. In the present invention, poly(tetramethylene glycol) and
poly(methyltetramethylene glycol) are preferred.
[0064] It is preferable for these long-chain polyols to have a
number-average molecular weight in a range of 1,500 to 5,000. By
using a long-chain polyol having a number-average molecular weight
within this range, golf balls made with a thermoplastic
polyurethane composition having excellent properties such as
resilience and manufacturability can be reliably obtained. The
number-average molecular weight of the long-chain polyol is more
preferably in a range of 1,700 to 4,000, and even more preferably
in a range of 1,900 to 3,000.
[0065] As used herein, "number-average molecular weight of the
long-chain polyol" refers to the number-average molecular weight
calculated based on the hydroxyl number measured in accordance with
JIS K-1557.
[0066] Any chain extender employed in the prior art relating to
thermoplastic polyurethane materials 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. In the present invention, an
aliphatic diol having 2 to 12 carbons is preferred, and
1,4-butylene glycol is more preferred.
[0067] Any polyisocyanate compound employed in the prior art
relating to thermoplastic polyurethane materials may be
advantageously used without particular limitation as the
polyisocyanate compound. For example, use may be made of one or
more selected from the group consisting of 4,4'-diphenylmethane
diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate,
p-phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene
diisocyanate, tetramethylxylene diisocyanate, hydrogenated xylylene
diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene
diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate,
norbornene diisocyanate, trimethylhexamethylene diisocyanate and
dimer acid diisocyanate. However, depending on the type of
isocyanate, the crosslinking 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
4,4'-diphenylmethane diisocyanate, which is an aromatic
diisocyanate.
[0068] It is most preferable for the thermoplastic polyurethane
serving as above component D to be a thermoplastic polyurethane
synthesized using a polyether polyol as the long-chain polyol,
using an aliphatic diol as the chain extender, and using an
aromatic diisocyanate as the polyisocyanate compound. It is
desirable, though not essential, for the polyether polyol to be a
polytetramethylene glycol having a number-average molecular weight
of at least 1,900, for the chain extender to be 1,4-butylene
glycol, and for the aromatic diisocyanate to be
4,4'-diphenylmethane diisocyanate.
[0069] The mixing ratio of active hydrogen atoms to isocyanate
groups in the above polyurethane-forming reaction can be adjusted
within a desirable range so as to make it possible to obtain a golf
ball which is composed of a thermoplastic polyurethane composition
and has various improved properties, such as rebound, spin
performance, scuff resistance and manufacturability. Specifically,
in preparing a thermoplastic polyurethane by reacting the above
long-chain polyol, polyisocyanate compound and chain extender, it
is desirable to use the respective components in proportions such
that the amount of isocyanate groups on the polyisocyanate compound
per mole of active hydrogen atoms on the long-chain polyol and the
chain extender is from 0.95 to 1.05 moles.
[0070] No particular limitation is imposed on the method of
preparing component (D). Production may be carried out by either a
prepolymer process or a one-shot process in which the long-chain
polyol, chain extender and polyisocyanate compound are used and a
known urethane-forming reaction is effected. Of these, a process in
which melt polymerization is carried out in a substantially
solvent-free state is preferred. Production by continuous melt
polymerization using a multiple screw extruder is especially
preferred.
[0071] A commercial product may be used as component (D).
Illustrative examples include products available under the trade
names Pandex T8295, Pandex T8290 and Pandex T8260 (DIC Bayer
Polymer, Ltd.).
[0072] Next, concerning the polyisocyanate compound used as
component E, it is essential that, in at least some portion thereof
within a single resin blend, all the isocyanate groups on the
molecule remain in an unreacted state. That is, polyisocyanate
compound in which all the isocyanate groups on the molecule are in
a completely free state should be present within a single resin
blend, and such a polyisocyanate compound may be present together
with a polyisocyanate compound in which a portion of the isocyanate
groups on the molecule are in a free state.
[0073] Various isocyanates may be used without particular
limitation as the polyisocyanate compound. Specific examples
include one or more selected from the group consisting of
4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate,
2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene
diisocyanate, 1,5-naphthylene diisocyanate, tetramethylxylene
diisocyanate, hydrogenated xylylene diisocyanate,
dicyclohexylmethane diisocyanate, tetramethylene diisocyanate,
hexamethylene diisocyanate, isophorone diisocyanate, norbornene
diisocyanate, trimethylhexamethylene diisocyanate and dimer acid
diisocyanate. Of the above group of isocyanates, using
4,4'-diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate
and isophorone diisocyanate is preferred for achieving a good
balance between the influence on moldability by, for example, the
rise in viscosity associated with reaction with the thermoplastic
polyurethane serving as component D, and the properties of the
resulting golf ball cover material.
[0074] In material (II), although not an essential ingredient, a
thermoplastic elastomer other than the above thermoplastic
polyurethane may be included as component F in addition to above
components D and E. Including this component F in the above resin
blend enables the flow properties of the resin blend to be further
improved and enables various properties required of golf ball cover
materials, such as resilience and scuff resistance, to be
enhanced.
[0075] This component F, which is a thermoplastic elastomer other
than the above thermoplastic polyurethane, is exemplified by one or
more thermoplastic elastomer selected from among polyester
elastomers, polyamide elastomers, ionomeric resins, styrene block
elastomers, hydrogenated styrene-butadiene rubbers,
styrene-ethylene/butylene-ethylene block copolymers and modified
forms thereof, ethylene-ethylene/butylene-ethylene block copolymers
and modified forms thereof, styrene-ethylene/butylene-styrene block
copolymers and modified forms thereof, ABS resins, polyacetals,
polyethylenes and nylon resins. The use of polyester elastomers,
polyamide elastomers and polyacetals is especially preferred
because the resilience and scuff resistance are enhanced, owing to
reactions with isocyanate groups, while at the same time a good
manufacturability is retained.
[0076] The relative proportions of above components D, E and F are
not subject to any particular limitation. However, to fully achieve
the advantageous effects of the invention, it is preferable for the
weight ratio among the respective components to be (D):(E):(F)
=100:2 to 50:0 to 50, and more preferably (D):(E):(F) =100:2 to
30:8 to 50.
[0077] In this invention, a single resin blend for forming the
cover is prepared by mixing together component D, component E, and
also optional component F. At this time, it is essential to select
the mixing conditions such that, of the polyisocyanate compound, at
least some polyisocyanate compound is present in which all the
isocyanate groups on the molecule remain in an unreacted state. For
example, treatment such as mixture in an inert gas (e.g., nitrogen)
or in a vacuum state must be furnished. The resin blend is then
injection-molded around a core which has been placed in a mold. To
smoothly and easily handle the resin blend, it is preferable for
the blend to be formed into pellets having a length of 1 to 10 mm
and a diameter of 0.5 to 5 mm. Sufficient isocyanate groups in an
unreacted state remain in these resin pellets; the unreacted
isocyanate groups react with component D or component F to form a
crosslinked material while the resin blend is being
injection-molded about the core, or due to post-treatment such as
annealing thereafter.
[0078] In addition, various optional additives may also be included
in this cover-forming resin blend. For example, pigments,
dispersants, antioxidants, light stabilizers, ultraviolet
absorbers, and parting agents may be suitably included.
[0079] The melt mass flow rate (MFR) of this resin blend at
210.degree. C. is not subject to any particular limitation.
However, to increase the flow properties and manufacturability, the
MFR is preferably at least 5 g/10 min, and more preferably at least
6 g/10 min. If the melt mass flow rate of the resin blend is too
low, the flow properties will decrease, which may cause
eccentricity during injection molding and may also lower the degree
of freedom in the thickness of the cover that can be molded. The
melt mass flow rate is a measured value obtained in accordance with
JIS-K7210 (1999 edition).
[0080] The method of molding the cover may involve feeding the
above resin blend to an injection-molding machine and injecting the
molten resin blend around the core. Although the molding
temperature in this case will vary depending on the type of
thermoplastic polyurethane, the molding temperature is generally
from 150 to 250.degree. C.
[0081] When injection molding is carried out, it is desirable
though not essential to carry out molding in a low-humidity
environment such as by purging with an inert gas (e.g., nitrogen)
or a low-moisture gas (e.g., low dew-point dry air), or vacuum
treating, some or all places on the resin paths from the resin feed
area to the mold interior. Illustrative, non-limiting, examples of
the medium used for transporting the resin include low-moisture
gases such as low dew-point dry air or nitrogen. By carrying out
molding in such a low-humidity environment, reaction by the
isocyanate groups is kept from proceeding before the resin has been
charged into the mold interior. As a result, polyisocyanate in
which the isocyanate groups are present in an unreacted state is
included to some degree in the molded resin material, thus making
it possible to reduce variable factors such as an unnecessary in
viscosity and enabling the real crosslinking efficiency to be
enhanced.
[0082] Techniques that may be used to confirm the presence of
polyisocyanate compound in an unreacted state within the resin
blend prior to injection molding about the core include those which
involve extraction with a suitable solvent that selectively
dissolves out only the polyisocyanate compound. An example of a
simple and convenient method is one in which confirmation is
carried out by simultaneous thermogravimetric and differential
thermal analysis (TG-DTA) measurement in an inert atmosphere. For
example, when the above-described single resin blend (material
(II)) is heated in a nitrogen atmosphere at a temperature ramp-up
rate of 10.degree. C./min, a gradual drop in the weight of
diphenylmethane diisocyanate can be observed from about 150.degree.
C. On the other hand, in a resin sample in which the reaction
between the thermoplastic polyurethane material and the isocyanate
mixture has been carried out to completion, a weight drop is not
observed from about 150.degree. C., but a weight drop can be
observed from about 230 to 240.degree. C.
[0083] After the above material (II) has been injection-molded to
form a cover, the properties as a golf ball cover can be
additionally improved by carrying out annealing so as to induce the
crosslinking reaction to proceed further. "Annealing," as used
herein, refers to aging the cover in a fixed environment for a
fixed length of time.
Ionomeric Resin Material
[0084] In the present invention, "ionomeric resin material" refers
to a resin composition which includes: 100 parts by weight of a
resin component composed of
[0085] a base resin containing (a) from 95 to 50 wt % of an
olefin-unsaturated carboxylic acid-unsaturated carboxylic acid
ester random copolymer and/or a metal salt thereof and (b) from 0
to 20 wt % of an olefin-unsaturated carboxylic acid random
copolymer and/or a metal salt thereof, and
[0086] (c) from 0 to 50 wt % of a thermoplastic block copolymer
composed of a crystalline polyolefin block and a
polyethylene/butylene random copolymer;
[0087] (d) from 5 to 170 parts by weight of a fatty acid and/or
fatty acid derivative having a molecular weight of 280 to 1,500;
and
[0088] (e) from 0.1 to 10 parts by weight of a basic inorganic
metal compound capable of neutralizing acid groups in components
(a) and (d), and, if necessary, component (b).
[0089] Components (a) to (e) are described below.
[0090] Component (a) and component (b) serve as the base resin of
the above resin composition. Component (a) is an olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester random copolymer
and/or metal salt thereof, and component (b) is an
olefin-unsaturated carboxylic acid random copolymer and/or a metal
salt thereof. In the present invention, either of above components
(a) and (b) may be used singly or both may used in combination.
[0091] Here, above component (a) has a weight-average molecular
weight (Mw) of preferably at least 100,000, more preferably at
least 110,000, and even more preferably at least 120,000, but
preferably not more than 200,000, more preferably not more than
190,000, and even more preferably not more than 170,000. The
weight-average molecular weight (Mw) to number-average molecular
weight (Mn) ratio for the copolymer is preferably at least 3, and
more preferably at least 4, with the upper limit being preferably
not more than 7, and more preferably not more than 6.5.
[0092] The olefin in component (a) generally has a number of
carbons that is at least 2, but not more than 8, and preferably not
more than 6. Illustrative examples of such olefins include
ethylene, propylene, butene, pentene, hexene, heptene and octene.
Ethylene is especially preferred.
[0093] Illustrative examples of the unsaturated carboxylic acid
include acrylic acid, methacrylic acid, maleic acid and fumaric
acid. Acrylic acid and methacrylic acid are especially
preferred.
[0094] The unsaturated carboxylic acid ester may be, for example, a
lower alkyl ester of an unsaturated carboxylic acid. Illustrative
examples include methyl methacrylate, ethyl methacrylate, propyl
methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate,
propyl acrylate and butyl acrylate. The use of butyl acrylate
(n-butyl acrylate, isobutyl acrylate) is especially preferred.
[0095] The random copolymer serving as component (a) may be
obtained by the random copolymerization of the above ingredients in
accordance with a known method. Here, the unsaturated carboxylic
acid content (acid content) within the random copolymer, although
not subject to any particular limitation, may be set to generally
at least 2 wt %, preferably at least 6 wt %, and more preferably at
least 8 wt %. It is recommended that the upper limit in the
unsaturated carboxylic acid content (acid content), although not
subject to any particular limitation, be generally not more than 25
wt %, preferably not more than 20 wt %, and more preferably not
more than 15 wt %. At a low acid content, the rebound may decrease,
whereas at a high acid content, the processability of the material
may decrease.
[0096] The copolymer of component (a) accounts for a proportion of
the overall base resin which is preferably from 95 to 50 wt %. The
lower limit of this proportion is preferably at least 60 wt %, more
preferably at least 70 wt %, and even more preferably at least 75
wt %. The upper limit to is preferably not more than 92 wt %, more
preferably not more than 89 wt %, and most preferably not more than
86 wt %.
[0097] The metal salt of the copolymer of component (a) may be
obtained by neutralizing some of the acid groups in the random
copolymer of component (a) with metal ions. Here, the metal ions
which neutralize the acid groups are exemplified by Na.sup.+,
K.sup.+, Li.sup.+, Zn.sup.++, Cu.sup.++, Mg.sup.++, Ca.sup.++,
Co.sup.++, Ni.sup.++ and Pb.sup.++. In the present invention, of
these, preferred use may be of Na.sup.+, Zn.sup.++, Mg.sup.++ and
Ca.sup.++ in particular, and Zn.sup.++ is even more recommended.
The degree of neutralization of the random copolymer by these metal
ions, while not subject to any particular limitation, is generally
at least 5 mol %, preferably at least 10 mol %, and especially at
least 20 mol %. It is recommended that the upper limit in the
degree of neutralization, while not subject to any particular
limitation, be generally not more than 95 mol %, preferably not
more than 90 mol %, and especially not more than 80 mol %. At a
degree of neutralization in excess of 95 mol %, the moldability may
decrease. On the other hand, at less than 5 mol %, it is necessary
to increase the amount in which the inorganic metal compound
serving as component (c) is added, which may present a drawback in
terms of cost. Such a neutralization product may be obtained by a
known method. For example, the neutralization product may be
obtained by introducing a metal ion compound, such as a formate,
acetate, nitrate, carbonate, bicarbonate, oxide, hydroxide or
alkoxide, into the random copolymer.
[0098] A commercial product may be used as component (a).
Illustrative examples of olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester random copolymers include
those available under the trade names Nucrel AN4318, Nucrel AN4319,
and Nucrel AN4311 (DuPont-Mitsui Polychemicals Co., Ltd.).
Illustrative examples of metal salts of olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester random copolymers
include those available under the trade names Himilan AM7316,
Himilan AM7331, Himilan 1855 and Himilan 1856 (DuPont-Mitsui
Polychemicals Co., Ltd.), and those available under the trade names
Surlyn 6320 and Surlyn 8120 (E.I. DuPont de Nemours and Co.,
Ltd.).
[0099] Next, it is recommended that the weight-average molecular
weight (Mw) of component (b) be preferably at least 100,000, more
preferably at least 110,000, and even more preferably at least
120,000, and that the upper limit thereof be preferably not more
than 200,000, more preferably not more than 190,000, and even more
preferably not more than 170,000. The weight-average molecular
weight (Mw) to number-average molecular weight (Mn) ratio for the
copolymer is preferably at least 3, and more preferably at least 4,
and the upper limit thereof is preferably not more than 7, and more
preferably not more than 6.5.
[0100] Here, the olefin in component (b) is generally an olefin in
which the number of carbons is at least 2 but not more than 8, and
preferably not more than 6. Illustrative examples include ethylene,
propylene, butene, pentene, hexene, heptene and octene. The use of
ethylene is especially preferred.
[0101] Illustrative examples of the unsaturated carboxylic acid in
component (b) include acrylic acid, methacrylic acid, maleic acid
and fumaric acid. Acrylic acid and methacrylic acid are especially
preferred.
[0102] In addition, the random copolymer serving as component (b)
may be obtained by the random copolymerization of the above
ingredients in accordance with a known method. Here, the
unsaturated carboxylic acid content (acid content) within the
random copolymer, while not subject to any particular limitation,
may be set to generally at least 2 wt %, preferably at least 6 wt
%, and more preferably at least 8 wt %. No particular limitation is
imposed on the upper limit in the unsaturated carboxylic acid
content (acid content), although it is recommended that this be
generally not more than 25 wt %, preferably not more than 20 wt %,
and more preferably not more than 15 wt %. At a low acid content,
there is a possibility that the rebound will decrease, whereas at a
high acid content, there is a possibility that the material
processability will decrease.
[0103] In the above case, the copolymer of component (b) accounts
for a proportion of the overall base resin which may be set to more
than 0, and may be set to preferably at least 1 wt %. The upper
limit, although not subject to any particular limitation, may be
set to not more than 20 wt %, preferably not more than 17 wt %,
more preferably not more than 10 wt %, even more preferably not
more than 8 wt %, and most preferably not more than 5 wt %.
[0104] The metal salt of the copolymer of component (b) may be
obtained by neutralizing some of the acid groups in the random
copolymer of component (b) with metal ions. Here, preferred use may
be made of, for example, Na.sup.+, K.sup.+, Li.sup.+, Zn.sup.++,
Cu.sup.++, Mg.sup.++, Ca.sup.++, Co.sup.++, Ni.sup.++ or Pb.sup.++,
as the metal ions which neutralize the acid groups. In the present
invention, of these, more preferred use may be made of Na.sup.+,
Li.sup.+, Zn.sup.++, Mg.sup.++ or Ca.sup.++. The use of Zn.sup.++
is especially recommended. The degree of neutralization of the
random copolymer by these metal ions, while not subject to any
particular limitation, may be set to generally at least 5 mol %,
preferably at least 10 mol %, and especially at least 20 mol %. It
is recommended that the upper limit in the degree of
neutralization, while not subject to any particular limitation, be
set to generally not more than 95 mol %, preferably not more than
90 mol %, and especially not more than 80 mol %. At a degree of
neutralization in excess of 95 mol %, the moldability may decrease.
On the other hand, at less than 5 mol %, there arises a need to
increase the amount in which the inorganic metal compound serving
as component (c) is added, which may present a drawback in terms of
cost. Such a neutralization product may be obtained by a known
method. For example, the neutralization product may be obtained by
introducing a metal ion compound, such as a formate, acetate,
nitrate, carbonate, bicarbonate, oxide, hydroxide or alkoxide, into
the random copolymer.
[0105] A commercial product may be used as component (b).
Illustrative examples include those available under the trade names
Nucrel 1560, Nucrel 1525 and Nucrel 1035 (DuPont-Mitsui
Polychemicals Co., Ltd.). Illustrative examples of metal salts of
the olefin-unsaturated carboxylic acid random copolymer include
those available under the trade names Himilan 1605, Himilan 1601,
Himilan 1557, Himilan 1705 and Himilan 1706 (DuPont-Mitsui
Polychemicals Co., Ltd.), those available under the trade names
Surlyn 7930 and Surlyn 7920 (E.I. DuPont de Nemours and Co., Ltd.),
and those available under the trade names Escor 5100 and Escor 5200
(ExxonMobil Chemical).
[0106] Component (c) is a thermoplastic block copolymer composed of
a crystalline polyolefin block and a polyethylene/butylene random
copolymer. This component (c) is exemplified by thermoplastic block
copolymers composed of a crystalline polyethylene block (E) as a
hard segment and a block of a relatively random copolymer of
ethylene and butylene (EB) as a soft segment. Preferred use may be
made of block copolymers having a molecular structure with a hard
segment at one or both ends, such as block copolymers having an
E-EB or E-EB-E structure.
[0107] Such a component (c) may be obtained by hydrogenating a
polybutadiene. Here, the polybutadiene used in hydrogenation is
preferably one in which bonding within the butadiene structure is
characterized by a 1,4-bond content in the butadiene structure as a
whole of from 95 to 100 wt %, and in which from 50 to 100 wt %, and
preferably from 80 to 100 wt %, of the 1,4-bonds are present as
block-like regions.
[0108] The above-mentioned E-EB-E type thermoplastic block
copolymer is preferably one obtained by hydrogenating a
polybutadiene having at both ends of the molecular chain
1,4-polymerization products which are rich in 1,4-bonds and having
an intermediate region where 1,4-bonds and 1,2-bonds are
intermingled. The degree of hydrogenation (conversion of double
bonds on the polybutadiene to saturated bonds) in the polybutadiene
hydrogenate is preferably from 60 to 100%, and more preferably from
90 to 100%. Too low a degree of hydrogenation may give rise to
undesirable effects such as gelation in the blending step with
other components such as an ionomeric resin and, when the golf ball
has been formed, may lead to a poor durability to impact.
[0109] In the block copolymer having an E-EB or E-EB-E molecular
structure with a hard segment at one or both ends that may be
advantageously used as the thermoplastic block copolymer, the
content of the hard segments is preferably from 10 to 50 wt %. If
the hard segment content is too high, the cover may lack sufficient
softness, making it difficult to effectively achieve the objects of
the invention. On the other hand, if the hard segment content is
too low, the blend may have a poor moldability.
[0110] The thermoplastic block copolymer has a melt mass flow
index, at a test temperature of 230.degree. C. and a test load of
21.2 N, of preferably from 0.01 to 15 g/10 min, and more preferably
from 0.03 to 10 g/10 min. Outside of this range, problems such as
weld lines, sink marks and short shots may arise during injection
molding. Moreover, it is preferable for the thermoplastic block
copolymer to have a surface hardness of from 10 to 50. If the
surface hardness is too low, the golf ball may have a decreased
durability to repeated impact. On the other hand, if the surface
hardness is too high, a blend of the thermoplastic block copolymer
with an ionomeric resin may have a decreased rebound. The
thermoplastic block copolymer has a number-average molecular weight
of preferably from 30,000 to 800,000.
[0111] A commercial product may be used as component (c).
Illustrative examples include those available under the trade names
Dynaron 6100P, Dynaron 6200P and Dynaron 6201B (JSR Corporation).
Of these, Dynaron 6100P, which is a block polymer having
crystalline olefin blocks at both ends, is especially preferred for
use in the present invention. These olefinic thermoplastic
elastomers may be used singly or as mixtures of two or more
thereof.
[0112] In cases where component (c) is included in the resin
component, the proportion of the overall resin component accounted
for by component (c) may be set to more than 0, and is preferably
set to at least 5 wt %, more preferably at least 8 wt %, even more
preferably at least 11 wt %, and most preferably at least 14 wt %.
The upper limit, while not subject to any particular limitation,
may be set to preferably not more than 50 wt %, more preferably not
more than 40 wt %, even more preferably not more than 30 wt %, and
most preferably not more than 20 wt %.
[0113] Component (d) is a fatty acid or fatty acid derivative
having a molecular weight of at least 280 but not more than 1,500
whose purpose is to enhance the flow properties of the resin
composition. It has a molecular weight which is very small compared
with those of components (a) to (c), and helps to significantly
decrease the melt viscosity of the mixture. Also, because the fatty
acid (or fatty acid derivative) of component (d) has a molecular
weight of at least 280 but not more than 1,500 and has a high
content of acid groups (or derivative moieties thereof), its
addition results in little loss of rebound.
[0114] The fatty acid or fatty acid derivative serving as component
(d) may be an unsaturated fatty acid or fatty acid derivative
having a double bond or triple bond in the alkyl moiety, or it may
be a saturated fatty acid or fatty acid derivative in which all the
bonds in the alkyl moiety are single bonds. It is recommended that
the number of carbon atoms on the molecule be generally at least
18, with an upper limit of not more than 80, and especially not
more than 40. Too few carbons may make it impossible to achieve an
improved heat resistance and may also set the acid group content so
high as to cause the acid groups to interact with acid groups
present in the base resin, diminishing the flow-improving effects.
On the other hand, too many carbons increases the molecular weight,
as a result of which significant flow-improving effects may not
appear, which may make the material difficult to use.
[0115] Specific examples of fatty acids that may be used as
component (d) include stearic acid, 12-hydroxystearic acid, behenic
acid, oleic acid, linoleic acid, linolenic acid, arachidic acid and
lignoceric acid. Of these, preferred use may be made of stearic
acid, arachidic acid, behenic acid, lignoceric acid and oleic
acid.
[0116] Fatty acid derivatives are exemplified by derivatives in
which the proton on the acid group of the fatty acid has been
substituted. Exemplary fatty acid derivatives of this type include
metallic soaps in which the proton has been substituted with a
metal ion. Metal ions that may be used in such metallic soaps
include Li.sup.+, Ca.sup.++, Mg.sup.++, Zn.sup.++, Mn.sup.++,
Al.sup.+++, Ni.sup.++, Fe.sup.++, Fe.sup.+++, Cu.sup.++, Sn.sup.++,
Pb.sup.++ and Co.sup.++. Of these, Ca.sup.++, Mg.sup.++ and
Zn.sup.++ are especially preferred.
[0117] Specific examples of fatty acid derivatives that may be used
as component (d) include magnesium stearate, calcium stearate, zinc
stearate, magnesium 12-hydroxystearate, calcium 12-hydroxystearate,
zinc 12-hydroxystearate, magnesium arachidate, calcium arachidate,
zinc arachidate, magnesium behenate, calcium behenate, zinc
behenate, magnesium lignocerate, calcium lignocerate and zinc
lignocerate. Of these, magnesium stearate, calcium stearate, zinc
stearate, magnesium arachidate, calcium arachidate, zinc
arachidate, magnesium behenate, calcium behenate, zinc behenate,
magnesium lignocerate, calcium lignocerate and zinc lignocerate are
preferred.
[0118] The amount of component (d) included per 100 parts by weight
of the resin component is at least 5 parts by weight, preferably at
least 20 parts by weight, more preferably at least 50 parts by
weight, and even more preferably at least 85 parts by weight. The
upper limit in the amount included per 100 parts by weight of the
resin component is not more than 170 parts by weight, preferably
not more than 150 parts by weight, more preferably not more than
130 parts by weight, and even more preferably not more than 110
parts by weight.
[0119] Use may also be made of known metallic soap-modified
ionomers (see, for example, U.S. Pat. No. 5,312,857, U.S. Pat. No.
5,306,760 and International Disclosure WO 98/46671) when using
above components (a) and (b).
[0120] The basic inorganic metal compound of component (e) is
included so as to neutralize acid groups in above component (a),
component (d) and, if necessary, component (b). When above
component (d) is not included, and in particular when a
metal-modified ionomeric resin alone (e.g., a metal soap-modified
ionomeric resin of the type mentioned in the foregoing patent
publications, alone) is heated and mixed, as mentioned below, the
metallic soap and unneutralized acid groups present on the ionomer
undergo exchange reactions, generating a fatty acid. Because this
fatty acid has a low thermal stability and readily vaporizes during
molding, it causes molding defects. Moreover, if the fatty acid
thus generated deposits on the surface of the molded material, it
substantially lowers paint film adhesion.
##STR00001## [0121] (1) unneutralized acid group present on the
ionomeric resin [0122] (2) metallic soap [0123] (3) fatty acid
[0124] X: metal cation
[0125] To resolve such problems, a basic inorganic metal compound
which neutralizes the acid groups present in above components (a),
(b) and (d) is thus included as an essential component (component
(e)). By adding component (e), the acid groups in above components
(a), (b) and (d) are neutralized. Synergistic effects from the
inclusion of these respective components increase the thermal
stability of the resin composition while at the same time
conferring a good moldability, and also impart the excellent
property of enhancing rebound as a golf ball material.
[0126] It is recommended that component (e) be a basic inorganic
metal compound--preferably a monoxide or hydroxide--which is
capable of neutralizing acid groups in above components (a), (b)
and (d). Because such compounds have a high reactivity with the
ionomeric resin and the reaction by-products contain no organic
matter, the degree of neutralization of the resin composition can
be increased without a loss of thermal stability.
[0127] The metal ions used here in the basic inorganic metal
compound are exemplified by Li.sup.+, Na.sup.+, K.sup.+, Ca.sup.++,
Mg.sup.++, Zn.sup.++, Al.sup.+++, Ni.sup.+, Fe.sup.++, Fe.sup.+++,
Cu.sup.++, Mn.sup.++, Sn.sup.++, Pb.sup.++Co.sup.++. Illustrative
examples of the inorganic metal compound include basic inorganic
fillers containing these metal ions, such as magnesium oxide,
magnesium hydroxide, magnesium carbonate, zinc oxide, sodium
hydroxide, sodium carbonate, calcium oxide, calcium hydroxide,
lithium hydroxide and lithium carbonate. Of these, as noted above,
a monoxide or hydroxide is preferred. The use of magnesium oxide or
calcium hydroxide, which have high reactivities with ionomer
resins, is especially preferred in the present invention.
[0128] Component (e) is included in an amount, per 100 parts by
weight of the resin component, of from 0.1 to 10 parts by weight.
In this case, the lower limit is preferably at least 0.5 part by
weight, more preferably at least 0.8 part by weight, and even more
preferably at least 1 part by weight. The upper limit in the amount
included per 100 parts by weight of the resin component is not more
than 8 parts by weight, preferably not more than 5 parts by weight,
and more preferably not more than 4 parts by weight.
[0129] The above-described resin composition which is obtained by
blending components (a) to (e) can be provided with improved
thermal stability, moldability and resilience.
[0130] To this end, it is recommended that at least 70 mol %,
preferably at least 80 mol %, and more preferably at least 90 mol
%, of the acid groups in the resin composition be neutralized. A
high degree of neutralization more reliably suppresses the exchange
reactions that pose a problem in the above-described cases where
components (a) and (b) and the fatty acid (or fatty acid
derivative) alone are used, thus making it possible to prevent the
generation of fatty acids. As a result, a material can be obtained
which has a markedly increased thermal stability, a good
moldability, and a substantially higher resilience than
conventional ionomeric resins.
[0131] Here, with regard to neutralization of the above resin
composition, to more reliably achieve both a high degree of
neutralization and good flow properties, it is recommended that the
acid groups in the resin composition be neutralized with transition
metal ions and with alkali metal and/or alkaline earth metal ions.
Because transition metal ions have a weaker ionic cohesion than
alkali metal and alkaline earth metal ions, it is possible in this
way to neutralize some of the acid groups in the resin composition
and thus enable the flow properties to be significantly
improved.
[0132] Various additives may also be optionally included in the
above resin composition. Examples of additives which may be
suitably included are pigments, dispersants, antioxidants,
ultraviolet absorbers and optical stabilizers. Moreover, to further
improve the feel of the golf ball on impact, the resin composition
may also include various non-ionomeric thermoplastic elastomers.
Illustrative examples of such non-ionomeric thermoplastic
elastomers include styrene-based thermoplastic elastomers,
ester-based thermoplastic elastomers and urethane-based
thermoplastic elastomers. In this invention, the use of
styrene-based thermoplastic elastomers is especially preferred.
[0133] Use may be made of a known mixing apparatus when preparing
the above resin composition. For example, the above respective
ingredients may be mixed using a twin-screw extruder, a Banbury
mixer or a kneader. In such a case, the heating and mixing
conditions may be suitably selected according to the type of
material, and are not subject to any particular limitation. For
example, mixing may be carried out at a temperature of from 150 to
250.degree. C. The method of molding the cover using the above
resin composition is also not subject to any particular limitation.
For example, use may be made of an injection molding method or a
compression molding method. When injection molding is employed, the
process may involve placing a prefabricated core at a given
position in the injection mold, then introducing the above material
into the mold. When compression molding is employed, the process
may involve producing a pair of half cups from the above material,
covering the core with these half-cups, then applying pressure and
heat within a mold. If molding under heat and pressure is carried
out, the molding conditions used may be a temperature of from 120
to 170.degree. C. and a period of from 1 to 5 minutes.
[0134] The cover material used in the invention may be a known
cover material. Although not subject to any particular limitation,
preferred use may be made of the above-described polyurethane
material (I), polyurethane material (II) or an ionomeric resin
material.
[0135] In the inventive golf ball, by combining dimples which
satisfy the subsequently described specific parameters and are able
to achieve a relatively low trajectory with an inner cover layer
and an outer cover layer having the above-described specific
constructions, it is possible to greatly reduce the distance
traveled by the golf ball on shots taken at a high head speed and
also hold down the decrease in distance traveled on shots taken at
a low head speed. The parameters for the dimples formed in the
inventive golf ball are described in detail below.
[0136] In the present invention, dimples having the following
parameters (1) to (8) are formed on the surface of the cover made
of the above-described material. In cases where the surface of the
ball is subjected to finishing treatment (e.g., painting and
stamping) after the cover has been formed, parameters (1) to (8)
below are calculated based on the shape of the dimples on the
finished ball in which such treatment has been fully completed.
Dimple Parameter (1)
[0137] The total number of dimples is set in a range of at least
250 but not more than 500. In this case, the lower limit may be set
to preferably at least 280, more preferably at least 300, and even
more preferably at least 340. The upper limit may be set to
preferably not more than 450, more preferably not more than 420,
and even more preferably not more than 400. In this range, the golf
ball readily incurs lift, enabling the ball to travel farther,
particularly on shots with a driver.
Dimple Parameter (2)
[0138] To improve aerodynamic performance, the dimple surface
coverage (SR), defined as the sum of the surface areas on a
hypothetical sphere that are circumscribed by the edges of the
respective dimples as a proportion of the surface area of the
hypothetical sphere, is set to at least 70%. SR may be set to
preferably at least 71%, and more preferably at least 72%.
Dimple Parameter (3)
[0139] To improve the aerodynamic performance, the dimple volume
ratio (VR), defined as the sum of the volumes of individual dimple
spaces below a flat plane circumscribed by the edge of each dimple
on a golf ball as a proportion of the volume of the golf ball were
it to have no dimples on the surface (hypothetical sphere), is set
to at least 1.0%. It is recommended that VR be set to preferably at
least 1.1%, more preferably at least 1.15%, and even more
preferably at least 1.2%. The upper limit is not more than 1.5%,
preferably not more than 1.4%, and more preferably not more than
1.3%.
Dimple Parameter (4)
[0140] The number of dimple types, i.e., types of dimples of
mutually differing diameter DM and/or depth DP, is set to three or
more. Here, the number of types is set to preferably at least four,
and more preferably at least five. The upper limit is not more than
14 types, and preferably not more than 10 types. The number of
types of dimples is selected as appropriate in this way so as to
facilitate an to increase in the surface coverage SR specified in
the invention.
[0141] Here, referring to FIG. 2, the depth DP of a dimple is the
vertical distance from a hypothetical flat plane L, traced by
connecting the positions where the dimple meets land areas, to the
bottom (deepest position) of the dimple. The dimple diameter DM, as
shown in FIG. 2, is the diameter (span) between positions where the
dimple portion is tangent with land areas (non-dimple forming
portions), i.e., between the high points of the dimple portion. In
most cases, the golf ball has been subjected to painting or the
like. In such balls, the dimple diameter and depth refer to the
diameter and depth after the coat of paint has been applied.
Dimple Parameter (5)
[0142] To obtain a proper trajectory, the average dimple depth is
set to at least about 0.18 mm. It is recommended that the average
dimple depth be set to preferably at least about 0.19. The upper
limit is not more than about 1.0 mm, preferably not more than about
0.7 mm, and more preferably not more than about 0.5 mm. Here,
"average dimple depth" refers to the average of the depths of all
the dimples.
[0143] The average dimple diameter DM, while not subject to any
particular limitation, is preferably at least about 3.0 mm, more
preferably at least about 3.2 mm, and even more preferably at least
about 3.5 mm. The upper limit is preferably not more than about 7.5
mm, more preferably not more than about 6.5 mm, and even more
preferably not more than about 6 mm. Here, "average dimple diameter
DM" refers to the average of the diameters of all the dimples.
Dimple Parameter (6)
[0144] The ratio of the dimple diameter DM to the dimple depth DP,
or DM/DP, has an average value of not more than about 23. It is
recommended that this average value be preferably not more than
about 22, more preferably not more than about 21, and even more
preferably not more than about 20. The lower limit, while not
subject to any particular limitation, is preferably at least about
5, more preferably at least about 8, and even more preferably at
least about 10.
Dimple Parameter (7)
[0145] In the present invention, although not subject to any
particular limitation, when the dimples are divided into dimples Da
having a diameter of 3.7 mm or more and smaller dimples Db, the
(total number of Da)/(total number of Db) ratio is preferably set
to at least about 0.005 but not more than about 1. The lower limit
is more preferably at least about 0.01, even more preferably at
least about 0.1, still more preferably at least about 0.2, and most
preferably at least about 0.3. The upper limit is more preferably
not more than about 0.8, even more preferably not more than about
0.6, and most preferably not more than about 0.5.
[0146] The dimples Da having a diameter of at least 3.7 mm account
for a proportion of the total dimple volume which, while not
subject to any particular limitation, is preferably at least about
75%, more preferably at least about 78%, and even more preferably
at least about 80%. The upper limit value is preferably not more
than about 98%, more preferably not more than about 95%, and even
more preferably not more than about 92%.
[0147] The average diameter (Dm) of the Da dimples is preferably at
least about 3.7 mm, and more preferably at least about 3.8 mm. The
upper limit thereof is preferably not more than about 7 mm, and
more preferably not more than about 6 mm. The average depth (Dp) of
the Da dimples is preferably at least about 0.05 mm, and more
preferably at least about 0.1 mm. The upper limit thereof is
preferably not more than about 0.5 mm, and more preferably not more
than about 0.3 mm. The average volume of the Da dimples is
preferably at least about 0.8 mm.sup.3, and more preferably at
least about 1.0 mm.sup.3. The upper limit thereof is preferably not
more than about 3.0 mm.sup.3, and more preferably not more than
about 2.5 mm.sup.3. The ratio Dm/Dp for the Da dimples is
preferably at least about 7, and more preferably at least about 8,
and the upper limit thereof is preferably not more than about 25,
and more preferably not more than about 23. If the above numerical
value ranges are not satisfied, the low trajectory desired may not
be obtained, which may make it impossible to achieve the objects of
the invention.
[0148] The average diameter (Dm) of the Db dimples is preferably at
least about 1 mm, and more preferably at least about 2 mm. The
upper limit is preferably less than about 3.7 mm, and more
preferably not more than about 3.5 mm. The average depth (Dp) of
the Db dimples is preferably at least about 0.05 mm, and more
preferably at least about 0.1 mm. The upper limit thereof is
preferably not more than about 0.3 mm, and more preferably not more
than about 0.2 mm. The average volume of the Db dimples is
preferably at least about 0.2 mm.sup.3, and more preferably at
least about 0.3 mm.sup.3. The upper limit thereof is preferably not
more than about 1.5 mm.sup.3, and more preferably not more than
about 1.0 mm.sup.3. The ratio Dm/Dp for the Db dimples is
preferably at least about 10, and more preferably at least about
12. The upper limit thereof is preferably not more than about 30,
and more preferably not more than about 26. If the above numerical
value ranges are not satisfied, the low trajectory desired may not
be obtained, which may make it impossible to achieve the objects of
the invention.
Dimple Parameter (8)
[0149] To improve the distance a golf ball travels, it is desirable
for the ball to have a low coefficient of drag (CD) under
high-velocity conditions and a high coefficient of lift (CL) under
low-velocity conditions. Thus, in the present invention, with
regard to the low-velocity CL, it is critical for the coefficient
of lift CL when the ball is launched using an Ultra Ball Launcher
(UBL) at a Reynolds number of 70,000 and a spin rate of 2,000 rpm
to be maintained at 60% or more, and preferably at 65% or more, of
the coefficient of lift CL at a Reynolds number of 80,000 and a
spin rate of 2,000 rpm.
[0150] The shapes of the dimples are not limited to a circular
shape, and may also be suitably selected from among, for example,
polygonal, tear-shaped and oval shapes. Setting the number of
dimple types to at least three, and preferably at least five, makes
it possible for the dimples to cover a higher proportion of the
spherical surface. Also, by interspersing large and small dimples,
the surface coverage can be increased to the specified range.
Because this enables extreme fluctuations in the CL (coefficient of
lift) within the low-velocity region to be suppressed, the ball
trajectory can be made relatively low, thus making it easier to
elicit the advantageous effects of the invention.
[0151] The golf ball of the invention can be made to conform with
the Rules of Golf for competitive play, and may be formed to a
diameter of not less than 42.67 mm. It is suitable to set the
weight to generally not less than 45.0 g, and preferably not less
than 45.2 g, but not more than 45.93 g.
[0152] As described above, in this invention, it is possible to
substantially reduce the distance traveled by the ball on high HS
shots while at the same time holding down as much as possible the
decrease in distance traveled on low HS shots. As a result, a
superior golf ball for competitors having a low head speed can be
obtained.
EXAMPLES
[0153] The following Examples and Comparative Examples are provided
by way of illustration and not by way of limitation.
Examples 1 to 3, Comparative Examples 1 to 5
[0154] The rubber compositions shown in Table 1 were prepared, then
molded and vulcanized at 155.degree. C. for 15 minutes to produce
solid cores. Numbers in the table indicate parts by weight.
TABLE-US-00001 TABLE 1 A B C Polybutadiene rubber 1 100 100 0
Polybutadiene rubber 2 0 0 100 Zinc acrylate 30.0 31.5 28.0
Peroxide 1.2 1.2 1.2 Zinc oxide 4 4 4 Barium sulfate 20.1 21 18.7
Calcium carbonate 0 0 5 Antioxidant 0.1 0.1 0.1 Zinc salt of
pentachlorothiophenol 0.6 0.6 0 Specific gravity 1.186 1.194
1.186
[0155] Trade names of the materials in the table are as follows.
[0156] Polybutadiene rubber 1: [0157] Available under the trade
name "BR 730" from JSR Corporation. [0158] Polybutadiene rubber 2:
[0159] Available under the trade name "BR 01" from JSR Corporation.
[0160] Zinc acrylate: Available from Nihon Jyoryu Kogyo Co., Ltd.
[0161] Peroxide: 1,1-Bis(t-butylperoxy)cyclohexane; available under
the trade name "Perhexa C-40" from NOF Corporation. [0162] Zinc
oxide: Available from Sakai Chemical Industry Co., Ltd. [0163]
Barium sulfate: Available under the trade name "Precipitated Barium
Sulfate 100" from Sakai Chemical Industry Co., Ltd. [0164] Calcium
carbonate: [0165] Available under the trade name "Silver W" from
Shiraishi Calcium Kaisha, Ltd. [0166] Antioxidant: Available under
the trade name "Nocrac NS-6" from Ouchi Shinko Chemical Industry
Co., Ltd.
[0167] Next, the cover material shown in Table 2 below was
injection molded over the above core, thereby obtaining a
multi-piece solid golf ball in which the core is encased within an
inner cover layer and an outer cover layer of given
thicknesses.
TABLE-US-00002 TABLE 2 Cover material (pbw) D E F Himilan 1605 69 0
0 Dynaron 6100P 31 0 0 Pandex T8290 0 25 0 Pandex T8295 0 75 100
Calcium hydroxide 2.3 0 0 Polytail H 2 0 0 Behenic acid 18 0 0
Polyisocyanate compound 0 9 9 Thermoplastic elastomer 0 15 15
Titanium oxide 0 3.5 3.5 Polyethylene wax 0 1.5 1.5
[0168] Trade names of the materials in the table are as follows.
[0169] Himilan: An ionomeric resin available from DuPont-Mitsui
Polychemicals Co., Ltd. [0170] Dynaron 6100P: A hydrogenated
polymer available from JSR Corporation. [0171] Pandex: MDI-PTMG
type thermoplastic polyurethanes available from DIC Bayer Polymer.
[0172] Calcium hydroxide: [0173] Available under the trade name
"CLS-B" from Shiraishi Calcium Kaisha, Ltd. [0174] Polytail H: A
low-molecular-weight polyolefin polyol available from Mitsubishi
Chemical Corporation. [0175] Behenic acid: Available under the
trade name "NAA-222S" from NOF Corporation. [0176] Polyisocyanate
compound: [0177] 4,4'-Diphenylmethane diisocyanate. [0178]
Thermoplastic elastomer: [0179] Available under the trade name
"Hytrel 4001" from DuPont-Toray Co., Ltd. [0180] Titanium oxide:
Available under the trade name "Tipaque R550" from Ishihara Sangyo
Kaisha, Ltd. [0181] Polyethylene wax: Available under the trade
name "Sanwax 161P" from Sanyo Chemical Industries, Ltd.
[0182] Simultaneous with injection molding of the cover, numerous
dimples were formed on the surface of the cover, after which the
cover was spray-painted. In each example and comparative example,
the dimples on the surface of the ball after painting satisfied the
parameters shown in Tables 3 to 8 below. In these tables, the
dimple types designated as Da refer to dimples having a diameter of
3.7 mm or more, and the dimple types designated as Db refer to
dimples having a diameter of less than 3.7 mm.
[0183] With regard to the dimple patterns in the tables, the dimple
pattern for Examples 1 and 3 is shown in Table 3 (FIG. 3), the
pattern for Example 2 is shown in Table 4 (FIG. 4), the pattern for
Comparative Examples 1 and 5 is shown in Table 5 (FIG. 5), the
pattern for Comparative Example 2 is shown in Table 6 (FIG. 6), the
pattern for Comparative Example 3 is shown in Table 7 (FIG. 7), and
the pattern for Comparative Example 4 is shown in Table 8 (FIG. 8).
These diagrams are all top views of the ball. In the respective
examples, the bottom views of the ball have the same pattern as the
top views, and are thus omitted.
TABLE-US-00003 TABLE 3 Examples 1 Number and 3 of Diameter Depth
Volume Dimple type dimples (mm) (mm) (mm.sup.3) Da-I 40 4.1 0.21
1.53 Da-II 184 3.9 0.20 1.31 Db-I 96 3.3 0.16 0.73 Da-III 32 4.1
0.23 1.72 Da-IV 16 3.9 0.22 1.45 Db-II 16 3.2 0.15 0.62 Db-III 8
3.2 0.14 0.49
TABLE-US-00004 TABLE 4 Number Example 2 of Diameter Depth Volume
Dimple type dimples (mm) (mm) (mm.sup.3) Da-I 24 4.5 0.16 1.34
Da-II 150 4.3 0.16 1.22 Da-III 66 3.7 0.15 0.86 Db-I 18 2.7 0.12
0.36 Db-II 6 2.5 0.12 0.31 Da-IV 48 4.3 0.17 1.30 Da-V 12 3.8 0.16
0.96 Db-III 6 3.4 0.16 0.75 Db-IV 6 3.3 0.15 0.66
TABLE-US-00005 TABLE 5 Comparative Number Examples 1 and 5 of
Diameter Depth Volume Dimple type dimples (mm) (mm) (mm.sup.3) Da-I
24 4.7 0.15 1.25 Da-II 168 4.5 0.15 1.15 Da-III 48 3.9 0.15 0.85
Db-I 12 2.9 0.15 0.44 Db-II 12 2.6 0.11 0.24 Da-IV 30 4.4 0.16 1.20
Da-V 36 3.9 0.17 0.94 Db-III 8 3.5 0.16 0.70 Db-IV 6 3.4 0.15
0.61
TABLE-US-00006 TABLE 6 Comparative Number Example 2 of Diameter
Depth Volume Dimple type dimples (mm) (mm) (mm.sup.3) Da-I 12 4.6
0.16 1.28 Da-II 222 4.4 0.16 1.16 Da-III 36 3.8 0.15 0.80 Db-I 12
2.6 0.12 0.58 Da-IV 12 4.4 0.17 0.25 Da-V 24 3.8 0.16 1.25 Db-II 6
3.5 0.16 0.86 Db-III 6 3.4 0.15 0.7
TABLE-US-00007 TABLE 7 Comparative Number Example 3 of Diameter
Depth Volume Dimple type dimples (mm) (mm) (mm.sup.3) Da-I 228 4.3
0.17 1.06 Da-II 36 3.7 0.16 0.74 Db-I 12 2.5 0.12 0.23 Db-II 12 3.4
0.17 0.72 Da-III 42 4.3 0.18 1.14 Da-IV 24 3.7 0.17 0.80 Da-V 12
4.3 0.17 1.05 Da-VI 2 3.9 0.16 0.89
TABLE-US-00008 TABLE 8 Comparative Number Example 4 of Diameter
Depth Volume Dimple type dimples (mm) (mm) (mm.sup.3) Db-I 114 3.65
0.196 1.071 Da-I 114 4.0 0.153 1.013 Db-II 60 3.65 0.195 1.071
Db-III 12 2.5 0.167 0.431 Db-II 60 4.0 0.153 1.013
[0184] Various properties of the resulting multi-piece solid golf
balls were investigated as described below. The results are shown
in Table 9.
Deflection of Solid Core and Finished Ball
[0185] The solid core and the finished ball were placed on a hard
plate, and the deflection when compressed under a final load of
1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) was
measured.
Cover Hardness (Shore D Hardness)
[0186] The cover-forming material was formed under applied pressure
to a thickness of about 2 mm and the resulting sheet was held at
23.degree. C. for 2 weeks, following which the Shore D hardness of
the sheet was measured in accordance with ASTM D2240.
CL Ratio
[0187] The ratio of the coefficient of lift CL of a ball launched
using an Ultra Ball Launcher (UBL) at a Reynolds number of 70,000
and a spin rate of 2,000 rpm with respect to the coefficient of
lift CL of a ball launched at a Reynolds number of 80,000 and a
spin rate of 2,000 rpm was calculated.
Initial Velocity
[0188] The initial velocity of the ball 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 ball was held isothermally in a 23.+-.1.degree. C.
environment for at least 3 hours, then tested in a chamber at a
room temperature of 23.+-.2.degree. C. The ball was hit using a
250-pound (113.4 kg) head (striking mass) at an impact velocity of
143.8 ft/s (43.83 m/s). One dozen balls were each hit four times.
The time taken for the ball to traverse a distance of 6.28 ft (1.91
m) was measured and used to compute the initial velocity (m/s) of
the ball. This cycle was carried out over a period of about 15
minutes.
Flight Performance
[0189] A W#1 was mounted on a swing robot, and the distance
traveled by the ball when hit at a head speed (HS) of 54 m/s or 35
m/s was measured. The club used was a TOURSTAGE X-DRIVE 701 (2009
model; loft angle, 9.5.degree.) manufactured by Bridgestone Sports
Co., Ltd.
TABLE-US-00009 TABLE 9 Example Comparative Example 1 2 3 1 2 3 4 5
Core Formulation A A B C C C C A Diameter (mm) 37.3 37.3 36.5 37.3
37.3 37.3 37.3 37.3 Deflection (mm) 3.9 3.9 3.5 3.9 3.9 3.9 3.9 3.9
Inner Material D D D D D D D D Cover Hardness (Shore D) 56 56 56 56
56 56 56 56 Layer Thickness (mm) 1.7 1.7 2.1 1.7 1.7 1.7 1.7 1.7
Outer Material E E E E E E E E Cover Hardness (Shore D) 55 55 57 55
55 55 55 55 layer Thickness (mm) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
Cover hardness difference (Shore D) 1 1 -1 1 1 1 1 1 (inner layer -
outer layer) Dimples Number of dimple types 7 types 9 types 7 types
9 types 8 types 8 types 5 types 9 types Number of dimples 392 336
392 344 330 368 360 344 SR value (%) 72 76 72 80 78 76 71 80 VR
value (%) 1.20 1.06 1.20 0.90 0.88 0.93 0.90 0.90 Average DP (mm)
0.19 0.18 0.19 0.15 0.15 0.16 0.17 0.15 Average DM/DP 19.83 21.95
19.83 27.39 24.77 23.17 20.97 27.39 (Total number of Db)/ 0.44 0.12
0.44 0.12 0.08 0.07 1.07 0.12 (Total number of Da) Volume
proportion of 82 96 82 95 95 97 48 95 Da dimples ( % ) Low-velocity
CL ratio (%) 85 78 85 80 78 65 75 80 Ball Diameter (mm) 42.7 42.7
42.7 42.7 42.7 42.7 42.7 42.7 Weight (g) 45.3 45.3 45.3 45.3 45.3
45.3 45.3 45.3 Deflection (mm) 3.0 3.0 2.6 3.0 3.0 3.0 3.0 3.0
Initial velocity (m/s) 77.3 77.3 77.2 76.2 76.2 76.2 76.2 77.3
Flight HS Carry (m) 261.2 262.7 262.2 266.0 266.8 264.8 265.2 271.9
54 m/s Total 275.4 276.8 276.9 276.1 276.7 275.9 275.1 282.9
distance (m) HS Carry (m) 163.1 163.5 163.7 158.6 159.0 160.1 159.3
162.9 35 m/s Total 182.5 181.9 182.3 177.3 177.0 178.1 176.8 181.6
distance (m) Difference in carry (m) 98.1 99.2 98.5 107.4 107.8
104.7 105.9 109.0 Difference in total 92.9 94.9 94.6 98.8 99.7 97.8
98.3 101.3 distance (m)
[0190] In the above table, Comparative Examples 1 to 4 are
prior-art reduced-distance golf balls, and Comparative Example 5 is
a prior-art high-rebound golf ball. Here, on comparing the
reduced-distance golf balls of Examples 1 to 3 with those of
Comparative Examples 1 to 4, it can be seen that the balls in
Comparative Examples 1 to 4, owing to their lower rebound (initial
velocity) relative to the prior-art high-rebound golf ball of
Comparative Example 5, travel substantially reduced distances (both
the carry and the total distance) not only at a high head speed but
also at a low head speed. By contrast, it was confirmed that the
golf balls in Examples 1 to 3 of the invention, by having the same
rebound (initial velocity) as the high-rebound golf ball in
Comparative Example 5 and by combining therewith dimples which
satisfy specific parameters and can thus achieve a relatively low
trajectory, are more effective than the balls in Comparative
Examples 1 to 4 at suppressing the reduction in distance when hit
at a low head speed relative to the substantial reduction in
distance when hit at a high head speed. That is, the golf balls of
the present invention were confirmed to be golf balls for which the
difference in distance when hit at a high head speed versus when
hit at a low head speed is small, and which are thus able to
achieve a superior distance in the low head speed range while
holding down the distance traveled in the high head speed
range.
* * * * *