U.S. patent application number 12/782538 was filed with the patent office on 2011-11-24 for 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 | 20110287864 12/782538 |
Document ID | / |
Family ID | 44972927 |
Filed Date | 2011-11-24 |
United States Patent
Application |
20110287864 |
Kind Code |
A1 |
UMEZAWA; Junji ; et
al. |
November 24, 2011 |
GOLF BALL
Abstract
The invention provides a golf ball having a solid core, a cover
of at least one layer, and a plurality of dimples on a surface of
an outermost layer of the cover. The dimples number at least 250
but not more than 500, and have a volume ratio (VR) of from 1.20 to
1.60%. The outermost cover layer has a surface hardness, expressed
as the Shore D hardness, of from 58 to 75. The ball has a
deflection, when compressed under a final load of 1,275 N (130 kgf)
from an initial load state of 98 N (10 kgf), of from 4.0 to 6.0 mm.
This golf ball is able to substantially reduce the distance
traveled by the ball when struck at a high head speed, while at the
same time holding down the decrease in distance when struck at a
low head speed.
Inventors: |
UMEZAWA; Junji;
(Chichibu-shi, JP) ; Higuchi; Hiroshi;
(Chichibu-shi, JP) ; Sato; Katsunori;
(Chichibu-shi, JP) ; Nakagawa; Takuma;
(Chichibu-shi, JP) |
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Family ID: |
44972927 |
Appl. No.: |
12/782538 |
Filed: |
May 18, 2010 |
Current U.S.
Class: |
473/378 |
Current CPC
Class: |
A63B 37/0084 20130101;
A63B 37/0096 20130101; A63B 37/0034 20130101; A63B 37/0031
20130101; A63B 37/0017 20130101 |
Class at
Publication: |
473/378 |
International
Class: |
A63B 37/12 20060101
A63B037/12 |
Claims
1. A golf ball comprising a solid core, a cover of at least one
layer, and a plurality of dimples on a surface of an outermost
layer of the cover, wherein the dimples number at least 250 but not
more than 500 and have a volume ratio (VR) of from 1.20 to 1.60%,
the outermost cover layer has a surface hardness, expressed as the
Shore D hardness, of from 58 to 75, and the ball has a deflection,
when compressed under a final load of 1,275 N (130 kgf) from an
initial load state of 98 N (10 kgf), of from 4.0 to 6.0 mm.
2. The golf ball of claim 1, wherein the ball, under the conditions
of a head speed of 54 m/s, a ball initial velocity of 78.0.+-.0.5
m/s, a launch angle of 9.7.+-.0.5.degree. and an initial backspin
rate of 2,700.+-.100 rpm, has a total distance of not more than 290
yards.
3. The golf ball of claim 1, wherein the ball has a ratio of total
distance traveled when struck at a head speed of 54 m/s to total
distance traveled when struck at a head speed of 35 m/s (HS54/HS35)
of from 1.30 to 1.50.
4. The golf ball of claim 1, wherein the dimple volume ratio and
the deflection satisfy the relationship expressed by the formula:
4.times.VR+deflection=9.0 to 11.0.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a golf ball which is
composed of a solid core and a cover of at least one layer, and
which has a plurality of dimples on a surface of the outermost
layer of the cover. More specifically, the invention relates to a
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 minimizing the
degree of reduction in distance when struck at a low head
speed.
[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 trend toward regulation is accelerating for golf balls
as well, and there is a possibility that the upper limit in the
distance traveled by a golf ball under the conditions of use by a
professional golfer, i.e., under high HS conditions, will be
further restricted. Generally, if the distance a ball travels when
played under high HS conditions is reduced, the distance traveled
by the ball when played under the conditions of use by an ordinary
amateur player, i.e., under low HS conditions, also ends up
decreasing to a similar degree. Accordingly, there exists a desire
to satisfy the above restriction while at the same time minimizing
the decrease in distance by the golf ball when used by an ordinary
amateur player.
[0004] The distance traveled by a golf ball is generally held down
by limiting the initial velocity. However, in such cases, the
distance traveled decreases in about the same ratio both at high
head speeds and low head speeds. As a result, such balls have
significant drawbacks for low HS players.
[0005] 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 the decrease in
distance.
[0006] 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 having an optimized ball weight and
diameter.
[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 golf ball which is composed of a solid core and a cover
of at least one layer, and which has a plurality of dimples on a
surface of the outermost layer of the cover, by specifying, for the
dimples formed on the surface of the outermost cover layer, the
number of dimples and the dimple volume ratio (VR), and by
optimizing the surface hardness of the outermost cover layer and
the deflection of the ball as a whole, the distance traveled by the
ball when struck at a high head speed can be substantially reduced
while at the same time holding down the decrease in distance when
the ball is struck at a low head speed.
[0009] That is, unlike conventional methods which lower the ball
initial velocity or the core initial velocity, the golf ball of the
present invention is able, by combining low-trajectory dimples with
the internal structure of the ball, to substantially reduce the
distance traveled by the ball when struck at a high head speed
while at the same time holding down as much as possible, relative
to the reduction in distance at high head speed, the decrease in
the distance traveled by the ball when struck at a low head speed.
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 golf
balls.
[1] A golf ball comprising a solid core, a cover of at least one
layer, and a plurality of dimples on a surface of an outermost
layer of the cover, wherein the dimples number at least 250 but not
more than 500 and have a volume ratio (VR) of from 1.20 to 1.60%,
the outermost cover layer has a surface hardness, expressed as the
Shore D hardness, of from 58 to 75, and the ball has a deflection,
when compressed under a final load of 1,275 N (130 kgf) from an
initial load state of 98 N (10 kgf), of from 4.0 to 6.0 mm. [2] The
golf ball of [1], wherein the ball, under the conditions of a head
speed of 54 m/s, a ball initial velocity of 78.0.+-.0.5 m/s, a
launch angle of 9.7.+-.0.5.degree. and an initial backspin rate of
2,700.+-.100 rpm, has a total distance of not more than 290 yards.
[3] The golf ball of [1], wherein the ball has a ratio of total
distance traveled when struck at a head speed of 54 m/s to total
distance traveled when struck at a head speed of 35 m/s (HS54/HS35)
of from 1.30 to 1.50. [4] The golf ball of [1], wherein the dimple
volume ratio and the deflection satisfy the relationship expressed
by the formula:
4.times.VR+deflection=9.0 to 11.0.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0011] FIG. 1 is a cross-sectional view showing an example of the
internal structure of the golf ball according to the present
invention.
[0012] FIG. 2 is a schematic view illustrating a dimple used in the
present invention.
[0013] FIG. 3 is a top view showing a dimple pattern (I) used on
golf balls in examples of the invention and comparative
examples.
[0014] FIG. 4 is a top view showing a dimple pattern (II) used on a
golf ball in an example of the invention.
[0015] FIG. 5 is a top view showing a dimple pattern (III) used on
a golf ball in a comparative example.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The invention is described more fully below.
[0017] The golf ball of the invention is a multi solid golf ball
having a solid core (referred to below as simply the "core") and a
cover of at least one layer. A plurality of dimples are formed on a
surface of an outermost layer of the cover. By optimizing within
specific ranges the surface hardness of the outermost cover layer
and the deflection of the ball as a whole and combining therewith
dimples which satisfy the subsequently described specific
parameters, the distance traveled by the ball when struck at a high
head speed can be substantially reduced while holding down the
decrease in the distance traveled by the ball when struck at a low
head speed. 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.
[0018] The internal structure of the golf ball G of the present
invention need only have a core and a cover of at least one layer,
and may be suitably set without particular limitation within a
range that does not depart from the objects of the invention. For
example, when the ball is a three-piece solid golf ball having a
two-layer cover composed of an inner layer and an outer layer, as
shown in FIG. 1, the ball has a three-layer construction with at
least a core 1, an inner cover layer 2 which encases the core 1,
and an outer cover layer 3 which encases the inner cover layer 2.
When the ball has a multi-layer construction with a cover of two or
more layers, the cover layers are sometimes referred to
collectively herein as the "cover." That is, in the case of the
three-piece solid golf ball shown in FIG. 1, 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 subsequently described parameters of the invention.
It should be noted that, although FIG. 1 shows a three-layer
construction arrived at by forming a core, an inner cover layer 2
and an outer cover layer 3, as mentioned above, this arrangement
may be suitably modified within a range that does not depart from
the objects of the invention. For example, if necessary, the cover
may be formed of one layer or of three or more layers. Or the core
1 may be formed of a plurality of layers.
[0019] 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.
[0020] 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 of organosulfur compound 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.
[0021] The diameter of the core, although not subject to any
particular limitation, may be set to from 30 to 42 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 41 mm,
more preferably not more than 40 mm, even more preferably not more
than 39 mm, and most preferably not more than 38 mm.
[0022] The core deflection, i.e., the amount of deflection when
compressed under a final load of 1,275 N (130 kgf) from an initial
load state of 98 N (10 kgf), although not subject to any particular
limitation, may be set within a range of from 3.0 to 9.0 mm. In
this case, the lower limit value is preferably at least 3.5 mm,
more preferably at least 4.0 mm, and even more preferably at least
4.5 mm. The upper limit value may be set to preferably not more
than 8.0 mm, and more preferably not more than 7.0 mm. If the core
is too much harder than the above range (small deflection), a
sufficient distance-reducing effect may not be achievable on shots
taken at a high head speed. 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.
[0023] 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.
[0024] 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.
[0025] The golf ball G of the present invention has a cover of at
least one layer formed over the solid core 1. The number, material
hardness (Shore D) and thickness of the cover layers formed in this
invention are not subject to any particular limitation, and may be
set as appropriate within ranges that do not depart from the
objects of the invention. For example, when the three-piece solid
golf ball shown in FIG. 1 is manufactured by forming over the core
1 a two-layer cover composed of an inner cover layer 2 and an outer
cover layer 3, these parameters may be set as indicated below.
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.
[0026] First, the material hardness (Shore D) of the inner cover
layer, although not subject to any particular limitation, may be
set to at least 30, preferably at least 35, more preferably at
least 40, and most preferably at least 45. It is recommended that
the upper limit be not more than 66, preferably not more than 63,
and more preferably not more than 60. When the material hardness
(Shore D) of the inner cover layer is too high, the ball may have a
poor feel on impact.
[0027] 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.
[0028] The material hardness (Shore D) of the outer cover layer,
although not subject to any particular limitation, may be set to at
least 55, preferably at least 57, and more preferably at least 59.
It is recommended that the upper limit be not more than 70,
preferably not more than 67, and more preferably not more than 64.
If the material hardness (Shore D) 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.
[0029] 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.
[0030] In the present invention, the cover may be formed of a known
material, examples of which include, but are not limited to,
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.
[0031] 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 for the same, are
described in order below.
Polyurethane Material (I)
[0032] This material (I) is composed primarily of components A and
B below:
(A) a thermoplastic polyurethane material, (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.
[0033] 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.
[0034] Next, each of the above components is described.
[0035] 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 serving 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 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. From the standpoint of rebound resilience and
low-temperature properties, polytetramethylene glycol is especially
preferred. 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.
[0036] The chain extender employed is preferably one that has
hitherto been used in the art relating to 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.
[0037] The diisocyanate employed is preferably one that has
hitherto been used in the 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. 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.
[0038] 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.).
[0039] 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 that has
hitherto been used in the 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.
[0040] 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.
[0041] 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.
[0042] 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).
[0043] 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.
[0044] 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.
[0045] 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).
[0046] 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
differs with the type of thermoplastic polyurethane material (A),
although molding is generally carried out within a temperature
range of 150 to 250.degree. C.
[0047] 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)
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] Any polyisocyanate compound hitherto employed in the 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.
[0057] 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
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 polyisocyanate compound to be
4,4'-diphenylmethane diisocyanate.
[0058] 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.
[0059] 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.
[0060] 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.).
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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 over 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.
[0067] 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.
[0068] 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 K-7210 (1999 edition).
[0069] The method of molding the cover may involve feeding the
above resin blend to an injection-molding machine and injecting the
molten resin blend over 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.
[0070] 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 rise
in viscosity and enabling the real crosslinking efficiency to be
enhanced.
[0071] 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.
[0072] 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
[0073] In the present invention, "ionomeric resin material" refers
to a resin composition which is composed primarily of a metal salt
of an olefin-unsaturated carboxylic acid-unsaturated carboxylic
acid ester random copolymer and/or a metal salt of an
olefin-unsaturated carboxylic acid random copolymer.
[0074] The olefin generally has a number of carbons that 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. Ethylene is especially preferred.
[0075] Illustrative examples of the unsaturated carboxylic acid
include acrylic acid, methacrylic acid, maleic acid and to fumaric
acid. Acrylic acid and methacrylic acid are especially
preferred.
[0076] 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.
[0077] The random copolymer 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.
[0078] Some or all of the acid groups in the random copolymer are
neutralized with metal ions. Although the degree of neutralization
in this case is not subject to any particular limitation, it is
recommended that at least 20 mol %, preferably at least 30 mol %,
more preferably at least 40 mol %, and even more preferably at
least 70 mol %, of the acid groups be neutralized. The upper limit
in the degree of neutralization, although not subject to any
particular limitation, may be set to 100 mol % or less, preferably
95 mol % or less, and more preferably 90 mol % or less. At a degree
of neutralization below 20%, the rebound may decrease. 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, Na.sup.+, Li.sup.+, Zn.sup.++, Mg.sup.++ and
Ca.sup.++ are especially preferred.
[0079] No particular limitation is imposed on the content of the
above metal salt of a random copolymer (ionomeric resin), although
the metal salt is preferably included in an amount of from 100 to
50 wt % based on the overall resin composition. In this case, the
lower limit is more preferably at least 60 wt %, even more
preferably at least 70 wt %, and most preferably at least 80 wt %.
The upper limit is more preferably 95 wt % or less, and even more
preferably 90 wt % or less. In this invention, a known material may
be used as the ionomeric resin material. Specific examples include
those available from E.I. DuPont de Nemours & Co. under the
trade names HPF 1000 and HPF 2000, and the resin compositions
mentioned in U.S. patent application Ser. No. 12/340,790 (or U.S.
patent application Ser. No. 12/706,175). These may be used singly
or as mixtures of two or more thereof.
[0080] To further improve the feel of the ball on impact, various
non-ionomeric thermoplastic elastomers may also be included. Such
non-ionomeric thermoplastic elastomers are exemplified by
olefin-based thermoplastic elastomers, styrene-based thermoplastic
elastomers, ester-based thermoplastic elastomers and urethane-based
thermoplastic elastomers. In the present invention, the use of an
olefin-based thermoplastic elastomer is especially preferred. The
olefin-based thermoplastic elastomer is a thermoplastic block
copolymer having a crystalline polyolefin block and a
polyethylene/butylene random copolymer. This olefin-based
thermoplastic elastomer 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.
[0081] These may be obtained by, for example, 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 overall butadiene
structure 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] A commercial product may be used as the olefin-based
thermoplastic elastomer. 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.
[0086] 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.
[0087] 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 ionomeric resin
material.
[0088] In the golf ball of the invention, by specifying the surface
hardness of the outermost cover layer and the deflection of the
ball as a whole and also forming dimples which satisfy the
subsequently described specific parameters and are able to achieve
a relatively low trajectory, it is possible to greatly reduce the
distance traveled by the golf ball on shots taken at a high head
speed while also holding down the decrease in distance traveled by
the ball on shots taken at a low head speed. The parameters for the
dimples formed on the inventive golf ball are described in detail
below.
[0089] In the present invention, dimples having the following
parameters (1) to (3) are formed on the surface of the cover formed
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 (3)
below are calculated based on the shape of the dimples on the
finished ball in which such treatment has been entirely
completed.
Dimple Parameter (1)
[0090] 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 310. The upper limit may be set to
preferably not more than 450, more preferably not more than 420,
even more preferably not more than 400, and most preferably not
more than 350.
Dimple Parameter (2)
[0091] 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, while not subject to any particular
limitation, is set to preferably at least 70%. The SR may be set to
more preferably at least 71%, and even more preferably at least
72%.
Dimple Parameter (3)
[0092] To improve the aerodynamic performance, the dimple to 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 hypothetical
sphere were the golf ball to have no dimples on the surface, is set
to from 1.20 to 1.60%. The lower limit is preferably at least
1.22%, and more preferably at least 1.24%. The upper limit is
preferably not more than 1.55%, more preferably not more than
1.50%, and even more preferably not more than 1.46%. In cases where
the volume ratio is larger than the above range, the trajectory may
become too low, as a result of which the ball may not travel far
enough on shots taken at a low head speed. On the other hand, when
the volume ratio is smaller than the above range, a sufficient
distance-reducing effect may not be achieved on shots taken at a
high head speed.
[0093] The shapes of the dimples are not limited to circular
shapes, 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 coefficient of
lift (CL) 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.
[0094] 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.
[0095] The golf ball of the invention is composed of the
above-described core and the cover of at least one layer, and has a
plurality of dimples on a surface of the outermost layer of the
cover. The ball as a whole has a deflection, when compressed under
a final load of 1,275 N (130 kgf) from an initial load state of 98
N (10 kgf), of at least 4.0 mm, preferably at least 4.1 mm, more
preferably at least 4.2 mm, and even more preferably at least 4.3
mm. The deflection has an upper limit which is not more than 6.0
mm, preferably not more than 5.8 mm, more preferably not more than
5.6 mm, and even more preferably not more than 5.3 mm. If the
deflection is too small, the distance traveled by the ball on shots
taken a high head speed may be excessive, making it impossible to
achieve the reduction in distance on high HS shots that is the
object of the invention. On the other hand, if the deflection is
too large, the ball may have a poor durability to cracking and may
have an excessively soft feel on impact.
[0096] It is critical for the surface hardness of the outermost
cover layer (i.e., the surface hardness of the ball), expressed as
the Shore D hardness, to be at least 58, preferably at least 59,
more preferably at least 60, and even more preferably at least 61.
The upper limit value is set to not more than 75, and may be set to
preferably not more than 72, more preferably not more than 70, and
even more preferably not more than 68. A ball surface hardness
which is too low may worsen the scuff resistance, and a ball
surface hardness which is too high may worsen the durability to
cracking. As used herein, the ball surface hardness (Shore D) is a
value measured at a dimple-free land portion of the ball surface
with a type D durometer in accordance with ASTM-2240.
[0097] The initial velocity of the ball, as measured using an
initial velocity measuring apparatus of the same type as the USGA
drum rotation-type initial velocity instrument, although not
subject to any particular limitation, is preferably from 72.0 to
77.7 m/s. The lower limit value is more preferably at least 74.0
m/s, and even more preferably at least 75.0 m/s. The upper limit
value is more preferably not more than 77.6 m/s, and even more
preferably not more than 77.4 m/s.
[0098] In the golf ball of the invention, although not subject to
any particular limitation, from the standpoint of suppressing the
reduction in distance on shots taken at a low head speed while
markedly reducing the distance on shots taken at a high head speed,
it is preferable for the dimple volume ratio and the deflection
described above to satisfy the relationship expressed by the
formula:
4.times.VR+deflection=9.0 to 11.0.
When the relationship between the dimple volume ratio and the
deflection does not satisfy the above formula, a sufficient
distance-reducing effect may not be achieved on shots taken at a
high head speed, in addition to which a good feel and a sufficient
durability to cracking may not be attained. In the present
invention, the above formula serves as an indicator representing a
proper relationship between the dimples and the ball construction
that ensures the distance traveled by the ball when struck at a low
head speed while suppressing the distance traveled when struck at a
high head speed.
[0099] As explained above, the golf ball of the invention greatly
reduces the distance traveled by the ball on shots taken at a high
head speed. In such cases, although not subject to any particular
limitation, it is preferable for the ball, under the conditions of
a head speed of 54 m/s, a ball initial velocity of 78.0.+-.0.5 m/s,
a launch angle of 9.7.+-.0.5.degree. and an initial backspin rate
of 2,700.+-.100 rpm, to have a total distance of not more than 290
yards.
[0100] Also, it is preferable for the difference in total distance
traveled by the ball depending on the magnitude of the head speed
to be small. Although not subject to any particular limitation, it
is recommended that the ball have a ratio of total distance
traveled when struck at a head speed of 54 m/s to total distance
traveled when struck at a head speed of 35 m/s (HS54/HS35) of at
least 1.30. The lower limit value in this ratio is preferably at
least 1.35, more preferably at least 1.38, and even more preferably
at least 1.40. The upper limit value is preferably not more than
1.49.
[0101] 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 minimizing the decrease in distance
traveled by the ball on low HS shots. As a result, there can be
obtained a superior golf ball for competitors having a low head
speed.
EXAMPLES
[0102] The following Examples and Comparative Examples are provided
by way of illustration and not by way of limitation.
Examples 1 to 5
Comparative Examples 1 to 5
[0103] 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 D E F Polybutadiene 75 85 85 100 65
100 rubber Isoprene rubber 25 15 15 0 20 0 Butyl rubber 0 0 0 0 15
0 Peroxide 1 0.6 0.6 0.6 0.6 0.6 0.6 Peroxide 2 0.6 0.6 0.6 0.6 0.6
0.6 Barium sulfate 22.4 24.4 21.8 22.4 20.7 21.7 Zinc oxide 4 4 4 4
4 4 Antioxidant 0.1 0.1 0.1 0.1 0.1 0.1 Zinc diacrylate 20 15 20 20
24 20 Zinc distearate 5.0 5.0 5.0 5.0 5.0 5.0 Calcium 10 10 0 10 10
0 carbonate Zinc salt 0 0 0 0 0 0.1 of penta- chlorothio- phenol
Specific gravity 1.205 1.205 1.162 1.205 1.205 1.162
[0104] Trade names of the materials in the table are as follows.
[0105] Polybutadiene rubber: Available under the trade name "BR 01"
from JSR Corporation. [0106] Isoprene rubber: Available under the
trade name "IR 2200" from JSR Corporation. [0107] Butyl rubber:
Available under the trade name "Bromobutyl 2222" from Japan Butyl
Co., Ltd. [0108] Peroxide 1: Dicumyl peroxide, available under the
trade name "Percumyl D" from NOF Corporation. [0109] Peroxide 2:
1,1-Bis(t-butylperoxy)cyclohexane, available under the trade name
"Perhexa C-40" from NOF Corporation. [0110] Barium sulfate:
Available under the trade name "Precipitated Barium Sulfate 100"
from Sakai Chemical Industry Co., Ltd. [0111] Zinc oxide: Available
from Sakai Chemical Industry Co., Ltd. [0112] Antioxidant:
Available under the trade name "Nocrac NS-6" from Ouchi Shinko
Chemical Industry Co., Ltd. [0113] Zinc diacrylate: Available from
Nihon Jyoryu Kogyo Co., Ltd. [0114] Zinc distearate: Available
under the trade name "Zinc Stearate G" from NOF Corporation.
[0115] Next, the cover material shown in Table 2 below was
injection-molded over the core, thereby obtaining a 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) (1) (2) (3) (4) HPF
2000 100 0 0 0 Himilan 1605 0 50 0 0 Himilan 1706 0 50 0 0 Pandex
T8290 0 0 0 75 Pandex T8295 0 0 100 25 Polyisocyanate compound 0 0
9 9 Thermoplastic elastomer 0 0 15 15 Titanium oxide 0 2 3.5 3.5
Polyethylene wax 0 0 1.5 1.5
[0116] Trade names of the materials in the table are as follows.
[0117] HPF 2000: An ionomeric resin available from E.I. DuPont de
Nemours & Co. [0118] Himilan: Ionomeric resins available from
DuPont-Mitsui Polychemicals Co., Ltd. [0119] Pandex: MDI-PTMG type
thermoplastic polyurethanes available from DIC Bayer Polymer.
[0120] Polyisocyanate compound: 4,4'-Diphenylmethane diisocyanate.
[0121] Thermoplastic elastomer: Available under the trade name
"Hytrel 4001" from DuPont-Toray Co., Ltd. [0122] Titanium oxide:
Available under the trade name [0123] "Tipaque R550" from Ishihara
Sangyo Kaisha, Ltd. [0124] Polyethylene wax: Available under the
trade name "Sanwax 161P" from Sanyo Chemical Industries, Ltd.
[0125] 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 7 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.
[0126] Here, referring to FIG. 2, the dimple depth (DP) in the
tables 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.
[0127] With regard to the dimple patterns in the tables, the dimple
patterns for Examples 1 to 3 and for Comparative
[0128] Example 3 are shown in Table 3 (FIG. 3), the pattern for
Example 4 is shown in Table 4 (FIG. 3), the pattern for Example 5
is shown in Table 5 (FIG. 4), the patterns for Comparative Examples
1 and 5 are shown in Table 6 (FIG. 3), and the patterns for
Comparative Examples 2 and 4 are shown in Table 7 (FIG. 5). 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 to 3, Number Comparative Example
3 of Diameter Depth Volume Dimple type dimples (mm) (mm) (mm.sup.3)
Da-I 12 4.6 0.23 1.97 Da-II 174 4.4 0.22 1.78 Da-III 18 4.0 0.21
1.40 Da-IV 6 3.8 0.20 1.21 Db-I 6 3.3 0.18 0.81 Db-II 36 2.4 0.13
0.32 Da-V 54 4.5 0.27 2.25 Db-III 6 3.4 0.16 0.75
TABLE-US-00004 TABLE 4 Number Example 4 of Diameter Depth Volume
Dimple type dimples (mm) (mm) (mm.sup.3) Da-I 12 4.6 0.29 2.54
Da-II 174 4.4 0.28 2.26 Da-III 18 4.0 0.27 1.79 Da-IV 6 3.8 0.26
1.52 Db-I 6 3.3 0.22 0.98 Db-II 36 2.4 0.13 0.32 Da-V 54 4.5 0.33
2.78 Db-III 6 3.4 0.16 0.75
TABLE-US-00005 TABLE 5 Number Example 5 of Diameter Depth Volume
Dimple type dimples (mm) (mm) (mm.sup.3) Da-I 40 4.0 0.24 1.88
Da-II 184 3.8 0.23 1.63 Db-I 96 3.2 0.22 1.07 Da-III 32 4.0 0.27
2.11 Da-IV 16 3.8 0.25 1.77 Db-II 16 3.1 0.20 0.91 Db-III 8 3.1
0.14 0.55
TABLE-US-00006 TABLE 6 Comparative Examples Number 1 and 5 of
Diameter Depth Volume Dimple type dimples (mm) (mm) (mm.sup.3) Da-I
12 4.6 0.17 1.47 Da-II 174 4.4 0.17 1.35 Da-III 18 4.0 0.16 1.05
Da-IV 6 3.8 0.16 0.93 Db-I 6 3.3 0.15 0.66 Db-II 36 2.4 0.11 0.26
Da-V 54 4.5 0.21 1.76 Db-III 6 3.4 0.16 0.75
TABLE-US-00007 TABLE 7 Comparative Examples Number 2 and 4 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
[0129] Various properties of the resulting golf balls were
investigated by the following methods. The results are shown in
Tables 8 and 9.
Deflection of Solid Core and Finished Ball
[0130] 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 Material Hardness (Shore D Hardness)
[0131] 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.
Ball Surface Hardness (Shore D Hardness)
[0132] Five finished balls were held isothermally at 23.degree. C.,
following which the surface of each was measured at two randomly
selected points in land areas without dimples. The measurements
were carried out with a type D durometer in accordance with ASTM
D-2240.
Initial Velocity
[0133] 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
[0134] A driver manufactured by Bridgestone Sports Co., Ltd.
(TOURSTAGE X-DRIVE 701 (2009 model; loft angle, 9.5.degree.)) 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
initial conditions here were set using Bridgestone Golf e5 balls
(manufactured by Bridgestone Sports Co., Ltd.), which have been
sold in the United States since November 2009. When this ball was
hit at a head speed of 54 m/s, the initial velocity was set to
78.0.+-.0.5 m/s, the launch angle was set to 9.7.+-.0.5.degree.,
and the initial backspin rate was set to 2,700.+-.100 rpm. When the
ball was hit at a head speed of 35 m/s, the initial velocity was
set to 53.0.+-.0.5 m/s, the launch angle was set to
14.0.+-.0.5.degree., and the initial backspin rate was set to
2,700.+-.100 rpm.
TABLE-US-00008 TABLE 8 Example 1 2 3 4 5 Core Formulation A B C D D
Diameter (mm) 37.3 37.3 37.3 37.3 37.3 Deflection (mm) 5.1 6.8 5.0
5.1 5.1 Inner Material (1) (1) (1) (1) (1) cover Material hardness
(Shore D) 48 48 48 48 48 layer Thickness (mm) 1.5 1.5 1.5 1.5 1.5
Outer Material (2) (2) (3) (2) (2) cover Material hardness (Shore
D) 63 63 57 63 63 layer Thickness (mm) 1.2 1.2 1.2 1.2 1.2 Dimples
Number of dimple types 8 types 8 types 8 types 8 types 7 types
Number of dimples 312 312 312 312 392 SR value (%) 74.4 74.4 74.4
74.4 71.6 VR value (%) 1.25 1.25 1.25 1.56 1.45 Ball Diameter (mm)
42.7 42.7 42.7 42.7 42.7 Weight (g) 45.3 45.3 45.3 45.3 45.3
Deflection (mm) 4.3 5.6 4.3 4.3 4.3 Surface hardness (Shore D) 66
66 59 66 66 Initial velocity (m/s) 75.6 75.6 75.6 77.3 77.3
Formula: 4 .times. VR + deflection 9.3 10.6 9.3 10.5 10.1 Flight HS
Carry (y) 260.5 249.7 258.0 248.0 251.2 54 m/s Total distance (y)
288.0 282.0 285.0 281.1 283.5 HS Carry (y) 168.0 164.0 166.3 170.2
171.0 35 m/s Total distance (y) 194.0 191.0 192.0 198.0 196.8
Difference in total distance (y) 94.0 91.0 93.0 83.1 86.7 Total
distance ratio HS54/HS35 1.48 1.48 1.48 1.42 1.44
TABLE-US-00009 TABLE 9 Comparative Example 1 2 3 4 5 Core
Formulation A A E F A Diameter (mm) 37.3 37.3 37.3 37.3 37.3
Deflection (mm) 5.1 5.1 4.0 5.0 5.1 Inner Material (1) (1) (1) (1)
(1) cover Material hardness (Shore D) 48 48 48 48 48 layer
Thickness (mm) 1.5 1.5 1.5 1.5 1.5 Outer Material (2) (2) (2) (4)
(2) cover Material hardness (Shore D) 63 63 63 50 63 layer
Thickness (mm) 1.2 1.2 1.2 1.2 1.2 Dimples Number of dimple types 8
types 9 types 8 types 9 types 8 types Number of dimples 312 336 312
336 312 SR value (%) 73.4 76.0 74.4 76.0 73.4 VR value (%) 0.94
1.06 1.25 1.06 0.94 Ball Diameter (mm) 42.7 42.7 42.7 42.7 42.7
Weight (g) 45.3 45.3 45.3 45.3 45.3 Deflection (mm) 4.3 4.3 3.4 4.3
4.3 Surface hardness (Shore D) 66 66 66 53 66 Initial velocity
(m/s) 75.6 75.6 75.6 77.3 75.6 Formula: 4 .times. VR + deflection
8.1 8.5 8.4 8.5 8.1 Flight HS Carry (y) 269.5 264.5 268.0 263.0
272.5 54 m/s Total distance (y) 291.1 288.1 292.5 289.0 294.1 HS
Carry (y) 166.6 163.6 170.5 168.0 168.4 35 m/s Total distance (y)
190.0 188.0 195.5 191.6 192.3 Difference in total distance (y)
101.1 100.1 97.0 97.4 101.8 Total distance ratio HS54/HS35 1.53
1.53 1.50 1.51 1.53
[0135] From the results in Tables 8 and 9, it was confirmed that,
compared with the golf balls in Comparative Examples 1 to 5, the
golf balls in Examples 1 to 5 of the present invention had a
decrease in distance on shots taken at low head speed that was
suppressed relative to the large reduction in distance on shots
taken at a high head speed. That is, the working examples of the
invention were confirmed to be golf balls which had a small
difference between the distance at high head speed and the distance
at low head speed, and were thus able to achieve a superior
distance in the low HS range while suppressing the distance in the
high HS range. The results obtained for the golf balls in
Comparative Examples 1 to 5 were as follows.
[0136] In Comparative Example 1, although the initial velocity was
held down, thus keeping the total distance on shots taken at a head
speed of 54 m/s at or below about 290 yards, because the dimple
volume ratio was small, the total distance on shots taken at a head
speed of 35 m/s also decreased significantly, resulting in a large
total distance ratio HS54/HS35.
[0137] In Comparative Example 2, although the initial velocity was
held down, thus keeping the total distance on shots taken at a head
speed of 54 m/s at or below about 290 yards, because the dimple
volume ratio was small, the total distance on shots taken at a head
speed of 35 m/s also decreased significantly, resulting in a large
total distance ratio HS54/HS35.
[0138] In Comparative Example 3, because the ball had a small
deflection, the total distance traveled by the ball when struck at
a head speed of 54 m/s exceeded 290 yards.
[0139] In Comparative Example 4, although the total distance on
shots taken at a head speed of 54 m/s was held to below 290 yards,
because the ball had a low surface hardness, the total distance on
shots taken at a head speed of 35 m/s also decreased significantly,
resulting in a large total distance ratio HS54/HS35.
[0140] In Comparative Example 5, because the dimple volume ratio
was small, the total distance on shots taken at a head speed of 54
m/s exceeded 290 yards, in addition to which the total distance
ratio HS54/HS35 was large.
* * * * *