U.S. patent application number 13/768804 was filed with the patent office on 2013-08-29 for multi-piece solid golf ball.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. The applicant listed for this patent is BRIDGESTONE SPORTS CO., LTD.. Invention is credited to Hiroshi Higuchi, Takuma Nakagawa, Katsunori Sato, Junji UMEZAWA.
Application Number | 20130225333 13/768804 |
Document ID | / |
Family ID | 49003491 |
Filed Date | 2013-08-29 |
United States Patent
Application |
20130225333 |
Kind Code |
A1 |
UMEZAWA; Junji ; et
al. |
August 29, 2013 |
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 numerous dimples on a surface thereof. The
ball is characterized by combining an inner cover layer and an
outer cover layer that are each formed to specific material
hardnesses and thicknesses with dimples which satisfy specific
conditions. This multi-piece solid 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; (Saitamaken,
JP) ; Sato; Katsunori; (Saitamaken, JP) ;
Higuchi; Hiroshi; (Saitamaken, JP) ; Nakagawa;
Takuma; (Saitamaken, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BRIDGESTONE SPORTS CO., LTD.; |
|
|
US |
|
|
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Family ID: |
49003491 |
Appl. No.: |
13/768804 |
Filed: |
February 15, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12757761 |
Apr 9, 2010 |
|
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13768804 |
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Current U.S.
Class: |
473/374 ;
473/384 |
Current CPC
Class: |
A63B 37/0064 20130101;
A63B 37/0066 20130101; A63B 37/002 20130101; A63B 37/0033 20130101;
A63B 37/0035 20130101; A63B 37/0019 20130101; A63B 37/0077
20130101; A63B 37/0096 20130101; A63B 37/0065 20130101; A63B
37/0083 20130101; A63B 37/0018 20130101; A63B 37/0092 20130101;
A63B 37/0006 20130101; A63B 37/0034 20130101; A63B 37/0084
20130101; A63B 37/0017 20130101; A63B 37/0004 20130101; A63B 37/008
20130101; A63B 37/0012 20130101; A63B 37/0075 20130101; A63B
37/0045 20130101; A63B 37/0043 20130101; A63B 37/0016 20130101;
A63B 37/0021 20130101; A63B 37/009 20130101; A63B 37/0031
20130101 |
Class at
Publication: |
473/374 ;
473/384 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
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
numerous dimples on a surface thereof, wherein the inner cover
layer has a thickness of from 0.8 to 3.0 mm and a material
hardness, in terms of Shore D hardness, of from 10 to 60, the outer
cover layer has a thickness of from 0.7 to 3.0 mm and a material
hardness, in terms of Shore D hardness, of from 45 to 62, and the
material hardness of the outer cover layer is higher than the
material hardness of the inner cover layer; the dimples number at
least 250 but not more than 50%, have a surface coverage (SR) of at
least 70% and a volume ratio (VR) of at least 1.06%, 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 an average 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 a coefficient of lift CL at a Reynolds number of
80,000 and a spin rate of 2,000 rpm.
2. The multi-piece solid golf ball of claim 1 wherein, letting Da
represent dimples having a diameter of at least 3.7 mm and Db
represent dimples having a diameter of less than 3.7 mm, the ratio
(total number of Db dimples)/(total number of Da dimples) is at
least about 0.005 but not more than about 1.
3. The multi-piece solid golf ball of claim 2, wherein the dimples
Da having a diameter 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 value
obtained by subtracting the material hardness of the inner cover
layer from the material hardness of the outer cover layer (outer
cover layer material hardness-inner cover layer material hardness)
is, in terms of Shore D hardness, at least 5 but not more than
50.
5. The multi-piece solid golf ball of claim 1, wherein the dimples
have an average edge angle of from 11 to 17 degrees.
6. The multi-piece solid golf ball of claim 1, wherein the
proportion of dimples having an edge angle of from 12 to 16 degrees
is more than 70% of the total number of dimples formed on the
surface of the ball.
7. The multi-piece solid golf ball of claim 1, wherein the value
obtained by subtracting the inner cover layer material hardness
from a surface hardness (Hs) of the core (Hs-inner cover layer
material hardness) is, in terms of Shore D hardness, greater than
-10 and less than +10.
8. The multi-piece solid golf ball of claim 1, wherein the value
obtained by subtracting the outer cover layer material hardness
from a surface hardness (Hs) of the core (Hs-outer cover layer
material hardness) is, in terms of Shore D hardness, at least -15
and not higher than +5.
9. The multi-piece solid golf ball of claim 1, wherein the ratio of
deflection by a sphere composed of the solid core encased by the
inner cover layer (inner cover layer-encased sphere) when
compressed under a final load of 1,275 N (130 kgf) from an initial
load state of 98 N (10 kgf) to deflection by the solid core when
compressed under a final load of 1,275 N (130 kgf) from an initial
load state of 98 N (10 kgf), which ratio is represented as (inner
cover layer-encased sphere deflection)/(solid core deflection), is
from 0.82 to 0.92.
10. The multi-piece solid golf ball of claim 1, wherein the ratio
of deflection by the ball when compressed under a final load of
1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) to
deflection by the solid core when compressed under a final load of
1,275 N (130 kgf) from an initial load state of 98 N (10 kgf),
which ratio is represented as (ball deflection)/(solid core
deflection), is from 0.72 to 0.79.
11. The multi-piece solid golf ball of claim 1, wherein the ratio
of deflection by the ball when compressed under a final load of
5,880 N (600 kgf) from an initial load state of 98 N (10 kgf) to
deflection by the ball when compressed under a final load of 1,275
N (130 kgf) from an initial load state of 98 N (10 kgf), which
ratio is represented as (600 kgf deflection/130 kgf deflection), is
from 3.2 to 3.7.
12. The multi-piece solid golf ball of claim 1, wherein the core
has a center hardness (Hc), a surface hardness (Hs) and a
cross-sectional hardness (Hm) at an intermediate position between
the core center and the core surface which, in terms of Shore D
hardnesses, satisfy the following conditions: Hm-Hc=0 to 7,
Hs-Hm=11 to 25, and Hs-Hc.gtoreq.16.
13. The multi-piece solid golf ball of claim 1, wherein the core
has a center hardness (Hc), a surface hardness (Hs) and a
cross-sectional hardness (Hm) at an intermediate position between
the core center and the core surface which, in terms of Shore D
hardnesses, satisfy the following condition:
Hs-Hm>(Hm-Hc).times.3.
14. The multi-piece solid golf ball of claim 1 wherein dimples Da
with a diameter of at least 3.7 mm have an average diameter of at
least 3.7 mm but not more than 6 mm, and dimples Db with a diameter
of less than 3.7 mm have an average diameter of at least 1 mm but
less than 3.7 mm.
15. The multi-piece solid golf ball of claim 1, wherein dimples Da
with a diameter of at least 3.7 mm have an average depth of from
0.05 to 0.5 mm, and dimples Db with a diameter of less than 3.7 mm
have an average depth of from 0.05 to 0.3 mm.
16. The multi-piece solid golf ball of claim 1, wherein dimples Da
with a diameter of at least 3.7 mm have an average volume of from
0.8 to 3.0 mm.sup.3, and dimples Db with a diameter of less than
3.7 mm have an average volume of from 0.2 to 1.5 mm.sup.3.
17. The multi-piece solid golf ball of claim 1, wherein dimples Da
with a diameter of at least 3.7 mm have an average diameter (Dm) to
average depth (Dp) ratio Dm/Dp of from 7 to 25, and dimples Db with
a diameter of less than 3.7 mm have an average diameter (Dm) to
average depth (Dp) ratio Dm/Dp of from 10 to 30.
18. The multi-piece solid golf ball of claim 1, wherein the cover
is formed of a material comprising: (A) a thermoplastic
polyurethane material, and (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.
19. The multi-piece solid golf ball of claim 1, wherein the cover
is formed of a material comprising: (D) a thermoplastic
polyurethane, and (E) a polyisocyanate compound.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of copending
application Ser. No. 12/757,761 filed on Apr. 9, 2010, the entire
contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 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 numerous 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.
[0003] 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, restrictions
have been placed on certain characteristics of a golf ball, such as
its size, weight and initial velocity, so as to limit excessive
ball travel of the sort that would result in a loss of fair
play.
[0004] 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.
[0005] As another approach, various 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.
[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 a value of
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.
[0007] In addition, JP-A 6-142228, JP-A 7-24084, JP-A 9-10358, JP-A
11-253578, JP-A 11-253579, JP-A 11-319149, JP-A 2000-70408, JP-A
2000-70409, JP-A 2000-70410 and JP-A 2000-70411 disclose golf balls
having a cover with a relatively soft inner layer and a relatively
hard outer layer.
[0008] 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
[0009] 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 numerous dimples on a surface thereof, by specifying the
thicknesses and material hardnesses (Shore D) of the inner cover
layer and the outer cover layer, and also the size relationship
between the material hardness of the inner cover layer and the
material hardness of the outer cover layer; by specifying, for the
dimples formed on the surface of the outer cover layer, the number
of dimples, the dimple surface coverage (SR), the dimple volume
ratio (VR), the dimple types, the average dimple depth, and the
dimple diameter-to-depth ratio (DM/DP); and by maintaining the
coefficient of lift CL at a Reynolds number of 70,000 and a spin
rate of 2,000 rpm at a specific ratio or more of the coefficient of
lift CL at a Reynolds number of 80,000 and a spin rate of 2,000
rpm, 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.
[0010] 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 internal structure (multilayer structure) of the ball, to
substantially reduce the distance traveled by 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 on high HS shots,
the reduction in the distance traveled by the ball 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.
[0011] Accordingly, the invention provides the following
multi-piece solid golf balls.
[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
numerous dimples on a surface thereof, wherein the inner cover
layer has a thickness of from 0.8 to 3.0 mm and a material
hardness, in terms of Shore D hardness, of from 10 to 60, the outer
cover layer has a thickness of from 0.7 to 3.0 mm and a material
hardness, in terms of Shore D hardness, of from 45 to 62, and the
material hardness of the outer cover layer is higher than the
material hardness of the inner cover layer; 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 1.06%, 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 an average 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 a coefficient of lift CL at a Reynolds number of
80,000 and a spin rate of 2,000 rpm. [2] The multi-piece solid golf
ball of [1] wherein, letting Da represent dimples having a diameter
of at least 3.7 mm and Db represent dimples having a diameter of
less than 3.7 mm, the ratio (total number of Db dimples)/(total
number of Da dimples) is at least about 0.005 but not more than
about 1. [3] The multi-piece solid golf ball of [2], wherein the
dimples Da having a diameter 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 [1], wherein the value obtained by subtracting
the material hardness of the inner cover layer from the material
hardness of the outer cover layer (outer cover layer material
hardness-inner cover layer material hardness) is, in terms of Shore
D hardness, at least 5 but not more than 50. [5] The multi-piece
solid golf ball of [1], wherein the dimples have an average edge
angle of from 11 to 17 degrees. [6] The multi-piece solid golf ball
of [1], wherein the proportion of dimples having an edge angle of
from 12 to 16 degrees is more than 70% of the total number of
dimples formed on the surface of the ball. [7] The multi-piece
solid golf ball of [1], wherein the value obtained by subtracting
the inner cover layer material hardness from a surface hardness
(Hs) of the core (Hs-inner cover layer material hardness) is, in
terms of Shore D hardness, greater than -10 and less than +10. [8]
The multi-piece solid golf ball of [1], wherein the value obtained
by subtracting the outer cover layer material hardness from a
surface hardness (Hs) of the core (Hs-outer cover layer material
hardness) is, in terms of Shore D hardness, at least -15 and not
higher than +5. [9] The multi-piece solid golf ball of [1], wherein
the ratio of deflection by a sphere composed of the solid core
encased by the inner cover layer (inner cover layer-encased sphere)
when compressed under a final load of 1,275 N (130 kgf) from an
initial load state of 98 N (10 kgf) to deflection by the solid core
when compressed under a final load of 1,275 N (130 kgf) from an
initial load state of 98 N (10 kgf), which ratio is represented as
(inner cover layer-encased sphere deflection)/(solid core
deflection), is from 0.82 to 0.92. [10] The multi-piece solid golf
ball of [1], wherein the ratio of deflection by the ball when
compressed under a final load of 1,275 N (130 kgf) from an initial
load state of 98 N (10 kgf) to deflection by the solid core when
compressed under a final load of 1,275 N (130 kgf) from an initial
load state of 98 N (10 kgf), which ratio is represented as (ball
deflection)/(solid core deflection), is from 0.72 to 0.79. [11] The
multi-piece solid golf ball of [1], wherein the ratio of deflection
by the ball when compressed under a final load of 5,880 N (600 kgf)
from an initial load state of 98 N (10 kgf) to deflection by the
ball when compressed under a final load of 1,275 N (130 kgf) from
an initial load state of 98 N (10 kgf), which ratio is represented
as (600 kgf deflection/130 kgf deflection), is from 3.2 to 3.7.
[12] The multi-piece solid golf ball of [1], wherein the core has a
center hardness (Hc), a surface hardness (Hs) and a cross-sectional
hardness (Hm) at an intermediate position between the core center
and the core surface which, in terms of Shore D hardnesses, satisfy
the following conditions:
Hm-Hc=0 to 7,
Hs-Hm=11 to 25, and
Hs-Hc.gtoreq.16.
[13] The multi-piece solid golf ball of [1], wherein the core has a
center hardness (Hc), a surface hardness (Hs) and a cross-sectional
hardness (Hm) at an intermediate position between the core center
and the core surface which, in terms of Shore D hardnesses, satisfy
the following condition:
Hs-Hm>(Hm-Hc).times.3.
[14] The multi-piece solid golf ball of [1] wherein dimples Da with
a diameter of at least 3.7 mm have an average diameter of at least
3.7 mm but not more than 6 mm, and dimples Db with a diameter of
less than 3.7 mm have an average diameter of at least 1 mm but less
than 3.7 mm. [15] The multi-piece solid golf ball of [1], wherein
dimples Da with a diameter of at least 3.7 mm have an average depth
of from 0.05 to 0.5 mm, and dimples Db with a diameter of less than
3.7 mm have an average depth of from 0.05 to 0.3 mm. [16] The
multi-piece solid golf ball of [1], wherein dimples Da with a
diameter of at least 3.7 mm have an average volume of from 0.8 to
3.0 mm.sup.3, and dimples Db with a diameter of less than 3.7 mm
have an average volume of from 0.2 to 1.5 mm.sup.3. [17] The
multi-piece solid golf ball of [1], wherein dimples Da with a
diameter of at least 3.7 mm have an average diameter (Dm) to
average depth (Dp) ratio Dm/Dp of from 7 to 25, and dimples Db with
a diameter of less than 3.7 mm have an average diameter (Dm) to
average depth (Dp) ratio Dm/Dp of from 10 to 30. [18] The
multi-piece solid golf ball of [1], wherein the cover is formed of
a material comprising:
[0012] (A) a thermoplastic polyurethane material, and
[0013] (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.
[19] The multi-piece solid golf ball of [1], wherein the cover is
formed of a material comprising:
[0014] (D) a thermoplastic polyurethane, and
[0015] (E) a polyisocyanate compound.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0016] 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.
[0017] FIG. 2 is a schematic view illustrating a dimple used in the
present invention.
[0018] 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.
[0019] 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.
[0020] FIG. 5 is a front view of a golf ball showing a dimple
pattern (III) used on a ball in a comparative example.
[0021] FIG. 6 is a front view of a golf ball showing a dimple
pattern (IV) used on a ball in a comparative example.
[0022] FIG. 7 is a front view of a golf ball showing a dimple
pattern (V) used on a ball in a comparative example.
[0023] FIG. 8 is a front view of a golf ball showing a dimple
pattern (VI) used on a ball in a comparative example.
[0024] FIG. 9 is a cross-sectional view for explaining the edge
angle of a dimple.
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 (sometimes referred to below as simply the
"core"), an inner cover layer and an outer cover layer. The outer
cover layer has a surface with numerous dimples formed thereon. By
combining an inner cover layer and an outer cover layer, each
formed to specific material hardnesses and specific thicknesses,
with dimples which satisfy the subsequently described specific
parameters, the distance traveled by the ball on shots taken at a
high HS can be substantially reduced while suppressing a decrease
in the distance traveled by the ball on shots taken 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 about 30
to 40 m/s.
[0027] The internal structure of the inventive golf ball G is
described. Referring to 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." Numerous dimples D are formed on the surface of the outer
cover layer 3; 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
be optionally 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 blended 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. 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, more preferably
not more than 39 mm, and even more preferably not more than 38.5
mm.
[0031] The core has a center hardness (Hc) which, although not
particularly limited, may be set to, in terms of Shore D hardness,
preferably at least 25, more preferably at least 28, and even more
preferably at least 31. The upper limit also is not particularly
limited and may be set to, in terms of Shore D hardness, preferably
not more than 50, more preferably not more than 45, and even more
preferably not more than 40. If the center hardness is too low, the
rebound may be too low, resulting in a less than desirable
distance, the feel at impact may be too soft, or the durability of
the ball to cracking on repeated impact may worsen. On the other
hand, if the center hardness is too high, the spin rate may rise
excessively, possibly resulting in a less than desirable distance,
or the feel at impact may be too hard.
[0032] The core has a surface hardness (Hs) which, although not
particularly limited, may be set to, in terms of Shore D hardness,
preferably at least 45, more preferably at least 48, and even more
preferably at least 51. The upper limit also is not particularly
limited and may be set to, in terms of Shore D hardness, preferably
not more than 70, more preferably not more than 65, and even more
preferably not more than 60. If the surface hardness is too low,
the rebound may be too low, resulting in a less than desirable
distance, the feel at impact may be too soft, or the durability of
the ball to cracking on repeated impact may worsen. On the other
hand, if the surface hardness is too high, the feel at impact may
be too hard or the durability to cracking on repeated impact may
worsen.
[0033] The core has a cross-sectional hardness (Hm) at an
intermediate position between the core center and the core surface
which, although not particularly limited, may be set to, in terms
of Shore D hardness, preferably at least 30, more preferably at
least 33, and even more preferably at least 36. The upper limit
also is not particularly limited and may be set to, in terms of
Shore D hardness, preferably not more than 55, more preferably not
more than 50, and even more preferably not more than 45. If the
cross-sectional hardness is too low, the rebound may be too low,
resulting in a less than desirable distance, or the durability to
cracking on repeated impact may worsen. On the other hand, if the
cross-sectional hardness is too high, the spin rate may rise
excessively, resulting in a less than desirable distance, or the
feel at impact may be too hard.
[0034] As used herein, "center hardness (Hc)" refers to the
hardness measured at the center of the cross-section obtained by
cutting the core in half (through the center), and "surface
hardness (Hs)" refers to the hardness measured at the surface of
the core (spherical surface). In addition, "cross-sectional
hardness (Hm) at an intermediate position between the core center
and the core surface" refers to the hardness measured at a point
midway between the core center and the core surface on the above
cross-section. Also, "Shore D hardness" refers to the hardness
measured using a type D durometer in general accordance with ASTM
D2240-95.
[0035] In this invention, the value Hm-Hc obtained by subtracting
the core center hardness (Hc) from the cross-sectional hardness
(Hm) at an intermediate position between the core center and core
surface, although not particularly limited, is preferably set to,
in terms of Shore D hardness, from 0 to 7. The upper limit in this
value may be set to, in terms of Shore D hardness, more preferably
not more than 6, and even more preferably not more than 5. The
lower limit may be set to, in terms of Shore D hardness, more
preferably at least 2, and even more preferably at least 3. If the
above value is too large, the durability to cracking on repeated
impact may worsen. On the other hand, if this value is too small,
the spin rate may rise excessively, as a result of which the
distance may be less than satisfactory.
[0036] The value Hs-Hm obtained by subtracting the cross-sectional
hardness (Hm) at an intermediate position between the core center
and core surface from the core surface hardness (Hs), although not
particularly limited, is preferably set to, in terms of Shore D
hardness, from 11 to 25. The upper limit in this value may be set
to, in terms of Shore D hardness, more preferably not more than 22,
and even more preferably not more than 20. The lower limit may be
set to, in terms of Shore D hardness, more preferably at least 12,
and even more preferably at least 15. If the above value is too
large, the durability to cracking on repeated impact may worsen. On
the other hand, if this value is too small, the spin rate may rise
excessively, as a result of which the distance may be less than
satisfactory.
[0037] The value Hs-Hc obtained by subtracting the core center
hardness (Hc) from the core surface hardness (Hs), although not
particularly limited, may be set to, in terms of Shore D hardness,
preferably at least 16, and more preferably at least 20. The upper
limit in this value, although not particularly limited, may be set
to, in terms of Shore D hardness, preferably not more than 40, and
more preferably not more than 30. If this value is too small, the
spin rate may rise excessively, as a result of which the distance
may be less than satisfactory.
[0038] In addition, the core center hardness (Hc), the core surface
hardness (Hs) and the cross-sectional hardness (Hm) at an
intermediate position between the core center and the core surface,
although not particularly limited, preferably satisfy, in terms of
Shore D hardnesses, the following condition:
Hs-Hm>(Hm-Hc).times.3.
In cases where the hardness relationship among the various parts of
the core departs from the above relationship, a good distance may
not be achieved at both high head speeds and low head speeds.
[0039] The core deflection, i.e., the amount of deflection by the
core when compressed under a final load of 1,275 N (130 kgf) from
an initial load of 98 N (10 kgf), while 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 at impact
may become too soft and the durability to cracking on repeated
impact may worsen.
[0040] 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.
[0041] In this invention, by using the above material to form the
solid core 1, a golf ball capable of achieving a stable trajectory
can be provided.
[0042] In the golf ball G of the invention, an inner cover layer 2
and an outer cover layer 3 are formed over the above solid core 1.
In this invention, the material hardnesses and thicknesses of each
of these layers are set as described below. Here, "material
hardness" refers to the hardness (Shore D) of a sheet of the cover
material that has been molded under applied pressure to a thickness
of about 2 mm, as measured using a type D durometer in general
accordance with ASTM D2240.
[0043] First, the material hardness of the inner cover layer is set
to, in terms of Shore D hardness, at least 10, and may be set to
preferably at least 20, more preferably at least 30, and most
preferably at least 40. The upper limit is set to, in terms of
Shore D hardness, not more than 60, and is recommended to be
preferably not more than 57, more preferably not more than 53, and
most preferably not more than 50. When the material hardness of the
inner cover layer is too low, a sufficient rebound is not obtained,
as a result of which, along with the reduction in the distance
traveled by the ball when struck at a high HS, the distance
traveled by the ball when struck at a low HS also substantially
decreases. On the other hand, if the material hardness is too high,
the feel of the ball at impact worsens.
[0044] The thickness of the inner cover layer is set to at least
0.8 mm, and may be set to preferably at least 1.0 mm, more
preferably at least 1.2 mm, and even more preferably at least 1.5
mm. The upper limit is not more than 3.0 mm, and is recommended to
be preferably not more than 2.5 mm, more preferably not more than
2.0 mm, and most preferably not more than 1.6 mm. When the inner
cover layer is too thin, the durability will worsen; when it is too
thick, the ball will have a poor feel at impact.
[0045] The deflection by a sphere composed of the above core
encased by the inner cover layer (inner cover layer-encased
sphere), 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 in the range of 2.0 to 5.5
mm. In this case, the lower limit is preferably at least 2.2 mm,
more preferably at least 2.5 mm, and even more preferably at least
2.8 mm. The upper limit may be set to preferably not more than 5.0
mm, more preferably not more than 4.5 mm, and even more preferably
not more than 4.0 mm. If the deflection is too small, the feel at
impact may be too hard. On the other hand, if the deflection is too
large, the feel at impact may be too soft and the durability to
cracking may be poor.
[0046] The material hardness of the outer cover layer, in terms of
Shore D hardness, is set to at least 45, and may be set to
preferably at least 50, more preferably at least 52, even more
preferably at least 54, and most preferably at least 55. The upper
limit is not more than 62, and is recommended to be preferably not
more than 61, and more preferably not more than 60. If the material
hardness of the outer cover layer is too low, the feel at impact
will be too soft or a sufficient rebound will not be obtained, as a
result of which, along with the reduction in distance traveled by
the ball when hit at a high HS, the distance traveled by the ball
when hit at a low HS also substantially decreases. On the other
hand, if the material hardness is too high, the durability worsens
or the feel of the ball at impact worsens.
[0047] The thickness of the outer cover layer is set to at least
0.7 mm, and may be set to preferably at least 1.0 mm, and more
preferably at least 1.2 mm. The upper limit is not more than 3.0
mm, preferably not more than 2.5 mm, more preferably not more than
2.0 mm, and even more preferably not more than 1.5 mm. If the outer
cover layer is too thin, a good feel at impact is not obtained. On
the other hand, if it is too thick, the durability worsens.
[0048] Moreover, in the present invention, the cover is formed so
that the material hardness of the outer cover layer is higher than
the material hardness of the inner cover layer. In this case, the
difference in hardness between the outer cover layer and the inner
cover layer (outer cover layer material hardness-inner cover layer
material hardness), although not subject to any particular
limitation, may be set so as to be preferably at least 5, more
preferably at least 6, and even more preferably at least 7. It is
recommended that the upper limit in this hardness difference be
preferably not more than 50, more preferably not more than 40, even
more preferably not more than 30, and most preferably not more than
20. If the hardness difference is too small, the feel at impact may
worsen; on the other hand, if it is too large, the durability may
worsen.
[0049] The ball having the above outer cover layer formed therein
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) which, although
not particularly limited, may be set in the range of 2.0 to 5.0 mm.
The lower limit in this case is preferably at least 2.2 mm, more
preferably at least 2.3 mm, and even more preferably at least 2.4
mm. The upper limit may be set to preferably not more than 4.5 mm,
more preferably not more than 4.0 mm, and even more preferably not
more than 3.5 mm. If the deflection is too small, the feel at
impact may be too hard. On the other hand, if the deflection is too
large, the feel at impact may be too soft or the durability to
cracking may be poor.
[0050] Moreover, the ball has a deflection when compressed under a
final load of 5,880 N (600 kgf) from an initial load state of 98 N
(10 kgf) which, although not particularly limited, may be set in
the range of 7.0 to 14.0 mm. The lower limit in this case is
preferably at least 8.0 mm, more preferably at least 8.5 mm, and
even more preferably at least 9.0 mm. The upper limit may be set to
preferably not more than 13.0 mm, more preferably not more than
12.0 mm, and even more preferably not more than 11.5 mm. If the
deflection is too small, the feel at impact may be too hard. On the
other hand, if the deflection is too large, the feel at impact may
be too soft or the durability to cracking may be poor.
[0051] The inner cover layer and the outer cover layer preferably
satisfy the following conditions in their relationship with the
solid core.
[0052] The value obtained by subtracting the material hardness of
the inner cover layer from the surface hardness (Hs) of the core,
which value is expressed as (Hs-inner cover layer material
hardness), although not particularly limited, is preferably set to,
in terms of Shore D hardness, greater than -10 and less than +10.
The upper limit, in terms of Shore D hardness, may be set to more
preferably not more than +7, and even more preferably not more than
+4. The lower limit, in terms of Shore D hardness, may be set to
more preferably at least -8, and even more preferably at least -5.
If this value is too large, the ball may have an insufficient
rebound or the spin rate of the ball may become too high. On the
other hand, if this value is too small, the feel at impact may
harden or the durability to cracking on repeated impact may
worsen.
[0053] The value obtained by subtracting the material hardness of
the outer cover layer from the surface hardness (Hs) of the core,
which value is expressed as (Hs-outer cover layer material
hardness), although not particularly limited, is preferably set to,
in terms of Shore D hardness, at least -15 and not higher than +5.
The upper limit, in terms of Shore D hardness, may be set to more
preferably not more than 2, and even more preferably not more than
0. The lower limit, in terms of Shore D hardness, may be set to
more preferably at least -10, and even more preferably at least -5.
If this value is too large, the ball may have an insufficient
rebound or the spin rate of the ball may become too high. On the
other hand, if this value is too small, the feel at impact may
become hard or the durability to cracking on repeated impact may
worsen.
[0054] In this invention, the ratio of deflection by a sphere
composed of the solid core encased by the inner cover layer (inner
cover layer-encased sphere) when compressed under a final load of
1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) to
deflection by the solid core when compressed under a final load of
1,275 N (130 kgf) from an initial load state of 98 N (10 kgf),
which ratio is represented as (inner cover layer-encased sphere
deflection)/(solid core deflection), is preferably from 0.82 to
0.92. The lower limit in this deflection ratio is more preferably
at least 0.84, and even more preferably at least 0.86. The upper
limit in this deflection ratio is more preferably not more than
0.90, and even more preferably not more than 0.88. If this
deflection ratio is too large, the ball rebound may be inadequate
or the spin rate may become too high. On the other hand, if this
value is too small, the feel at impact may harden or the durability
to cracking on repeated impact may worsen.
[0055] In addition, although not particularly limited, the ratio of
deflection by the ball when compressed under a final load of 1,275
N (130 kgf) from an initial load state of 98 N (10 kgf) to
deflection by the solid core when compressed under a final load of
1,275 N (130 kgf) from an initial load state of 98 N (10 kgf),
which ratio is represented as (ball deflection)/(solid core
deflection), is preferably from 0.72 to 0.79. The lower limit in
this deflection ratio is more preferably at least 0.74, and the
upper limit is preferably not more than 0.77. If this deflection
ratio is too large, the ball rebound may be inadequate or the spin
rate may become too high. On the other hand, if this value is too
small, the feel at impact may harden or the durability to cracking
on repeated impact may worsen.
[0056] Moreover, although not particularly limited, the ratio of
deflection by the ball when compressed under a final load of 5,880
N (600 kgf) from an initial load state of 98 N (10 kgf) to
deflection by the ball when compressed under a final load of 1,275
N (130 kgf) from an initial load state of 98 N (10 kgf), which
ratio is represented as (600 kgf deflection/130 kgf deflection), is
preferably from 3.2 to 3.7. The lower limit in this deflection
ratio is more preferably at least 3.3, and the upper limit is
preferably not more than 3.6. If this deflection ratio is too
large, the durability to cracking under repeated impact may worsen.
On the other hand, if this value is too small, the spin rate may
become high and the distance traveled by the ball may decrease
regardless of the head speed at which the ball is struck.
[0057] 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.
[0058] 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, and molding methods for the same, are
described in order below.
Polyurethane Material (I)
[0059] 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.
[0060] 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.
[0061] Next, each of the above components is described.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.).
[0066] 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.
[0067] 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.
[0068] 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 amount of the thermoplastic resin (B-2) is too
small, a greater amount of the isocyanate mixture (B) will have to
be added in order 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 amount of 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.
[0069] 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).
[0070] The above material (I) is composed primarily of the
thermoplastic polyurethane material (A) and the 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.
[0071] 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).
[0072] 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 the temperature
range of 150 to 250.degree. C.
[0073] 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 reactions have not yet proceeded to a sufficient
degree immediately after injection molding of the material (I), the
crosslinking reactions can be made to proceed further by carrying
out an annealing step after molding, in this way maintaining
characteristics which are useful for a golf ball cover.
"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)
[0074] 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.
[0075] 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.
[0076] 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 more
preferably at least 70%, of the total weight of the cover.
Components (D) and (E) are described in detail below.
[0077] 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.
[0078] 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.
[0079] It is preferable for these long-chain polyols to have a
number-average molecular weight in the 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 the range of 1,700 to 4,000, and even more preferably
in the range of 1,900 to 3,000.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.).
[0087] 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.
[0088] 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.
[0089] In Polyurethane 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.
[0090] 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.
[0091] 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.
[0092] 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.
[0093] 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.
[0094] 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).
[0095] 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.
[0096] When injection molding is carried out, it is desirable,
though not essential, to carry out such molding in a low-humidity
environment by subjecting some or all places on the resin paths
from the resin feed area to the mold interior to purging with an
inert gas such as nitrogen or a low-moisture gas such as low
dew-point dry air, or to vacuum treatment. Preferred, non-limiting,
examples of the medium used for transporting the resin under
applied pressure include low-moisture gases such as low dew-point
dry air or nitrogen gas. By carrying out molding in such a
low-humidity environment, the progression of reactions by
isocyanate groups before the resin blend is charged into the mold
interior is suppressed. By thus including, within the molded resin
material, polyisocyanate in which some isocyanate groups are
present in an unreacted state, it is possible to reduce variable
factors such as an undesirable rise in viscosity and to increase
the real crosslinking efficiency.
[0097] 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 (Polyurethane
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.
[0098] After the above Polyurethane 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
[0099] In the present invention, "ionomeric resin material" refers
to a resin composition which includes: 100 parts by weight of a
resin component composed of 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
[0100] (c) from 0 to 50 wt % of a thermoplastic block copolymer
composed of a crystalline polyolefin block and a
polyethylene/butylene random copolymer;
(d) from 5 to 170 parts by weight of a fatty acid or fatty acid
derivative having a molecular weight of 280 to 1,500; and (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).
[0101] Components (a) to (e) are described below.
[0102] 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 a 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.
[0103] 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.
[0104] 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.
[0105] 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.
[0106] 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.
[0107] 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.
[0108] 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 is preferably not more than 92 wt %, more
preferably not more than 89 wt %, and most preferably not more than
86 wt %.
[0109] 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.+, Li.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.
[0110] 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.).
[0111] 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.
[0112] 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.
[0113] 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.
[0114] 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.
[0115] 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 %.
[0116] 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.
[0117] 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).
[0118] 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.
[0119] 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.
[0120] 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.
[0121] 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.
[0122] The thermoplastic block copolymer has a melt mass flow rate,
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 resilience. The
thermoplastic block copolymer has a number-average molecular weight
of preferably from 30,000 to 800,000.
[0123] 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.
[0124] In cases where component (c) is included in the resin
component, the proportion of the total resin components 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 %.
[0125] 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.
[0126] 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.
[0127] 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.
[0128] 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.+++, 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.
[0129] 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.
[0130] 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.
[0131] 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).
[0132] 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##
[0133] 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.
[0134] 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.
[0135] 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.++ and 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.
[0136] 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.
[0137] The above-described resin composition which is obtained by
blending components (a) to (e) can be provided with improved
thermal stability, moldability and resilience. 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.
[0138] 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.
[0139] 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.
[0140] 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.
[0141] 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.
[0142] 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 specific constructions
described above, 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.
[0143] In the present invention, dimples having the following
parameters (1) to (10) 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 (10)
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)
[0144] The total number of dimples is set in a range of at least
250 but not more than 500. The lower limit in the number of dimples
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)
[0145] To improve aerodynamic performance, the dimple surface
coverage (SR), defined as the sum of the surface areas on the
surface of 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)
[0146] 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 1.06%. 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)
[0147] 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. The number of types may be set to preferably at least four,
and more preferably at least five. The upper limit is preferably
not more than 14 types, and more preferably not more than 10 types.
The number of types of dimples is selected as appropriate in this
way so as to facilitate an increase in the surface coverage SR
specified in the invention.
[0148] 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. In addition, as shown in
FIG. 2, the diameter DM of a dimple 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 is subjected to
surface treatment such as painting. 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)
[0149] 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 preferably not more than about 1.0 mm, more preferably not
more than about 0.7 mm, and even more preferably not more than
about 0.5 mm. Here, "average dimple depth" refers to the average of
the depths DP of all the dimples.
[0150] 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)
[0151] 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)
[0152] 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 dimples)/(total number of Db dimples) 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.
[0153] 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%.
[0154] 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 that is desired
may not be obtained, which may make it impossible to achieve the
objects of the invention.
[0155] 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 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 that is desired may not be obtained, which may make it
impossible to achieve the objects of the invention.
Dimple Parameter (8)
[0156] 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 when the ball is launched at a Reynolds
number of 80,000 and a spin rate of 2,000 rpm.
Dimple Parameter (9)
[0157] The dimples have an average edge angle of preferably at
least 11 degrees, more preferably at least 12 degrees, and even
more preferably at least 13 degrees. The upper limit is preferably
not more than 17 degrees, more preferably not more than 16 degrees,
and even more preferably not more than 15 degrees. If the average
edge angle is too large, the trajectory may become too low,
possibly resulting in too large a difference with a customary
trajectory. On the other hand, if the average edge angle is too
small, it may not be possible to obtain the effect of holding down
the decrease in distance traveled by the ball on shots at a low HS
while reducing the distance traveled on shots taken at a high HS.
As used herein, "average edge angle" refers to the average edge
angle for all the dimples.
Dimple Parameter (10)
[0158] It is recommended that the proportion of dimples having an
edge angle of from 12 to 16 degrees be preferably more than 70%,
more preferably at least 80%, and even more preferably at least
90%, of the total number of dimples formed on the ball surface. If
the proportion of such dimples is too small, it may not be possible
to obtain the effect of holding down the decrease in distance
traveled by the ball on shots at a low HS while reducing the
distance traveled on shots taken at a high HS.
[0159] The edge angle of a dimple is defined herein as follows.
Referring to FIG. 9, let us imagine over the dimple D a first
spherical surface (i.e., the spherical surface of the golf ball
were it to have no dimples thereon) Q.sub.1 prior to formation of
the dimple. Let us also imagine a second spherical surface Q.sub.2
which is centered at the center point of the golf ball and has a
radius 0.04 mm smaller than that of the first spherical surface
Q.sub.1. If we then draw tangents T and T' at points P and P' where
the second spherical surface Q.sub.2 intersects the wall of the
dimple D, the points E and E' where the tangents T and T' intersect
the first spherical surface Q.sub.1 represent the respective edges
of the dimple D. The angle .theta. between the line segment
(straight line) L connecting points E and E' determined in this way
and the tangents T and T' is the edge angle.
[0160] 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
can be given a relatively low trajectory, making it easier to
elicit the advantageous effects of the invention.
[0161] 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.
[0162] 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
[0163] 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
[0164] The rubber compositions shown in Table 1 were prepared, then
molded and vulcanized at 155.degree. C. for 15 minutes to produce
solid cores.
TABLE-US-00001 TABLE 1 A B C D E Formulation Polybutadiene rubber
(1) 100 100 100 100 (parts by Polybutadiene rubber (2) 100 weight)
Zinc acrylate 25.5 28.0 33.5 38.0 22.5 Peroxide (1) 0.6 0.6 1.1 1.1
0.6 Peroxide (2) 0.6 0.6 0.6 Zinc oxide 4 4 4 4 4 Barium sulfate
30.9 14.5 28 19.3 29.1 Calcium carbonate 12 2 5 Zinc stearate 5 5 5
5 Antioxidant 0.1 0.1 0.2 0.2 0.1 Zinc salt of 1 1
pentachlorothiophenol Sulfur 0.09 0.09 Specific gravity 1.226 1.196
1.226 1.196 1.226
[0165] Trade names of the materials in the table are as follows.
[0166] Polybutadiene rubber (1): Available under the trade name "BR
01" from JSR Corporation. [0167] Polybutadiene rubber (2):
Available under the trade name "BR 730" from JSR Corporation.
[0168] Zinc acrylate: Available from Nihon Jyoryu Kogyo Co., Ltd.
[0169] Peroxide (1): Dicumyl peroxide, available under the trade
name "Percumyl D" from NOF Corporation. [0170] Peroxide (2):
1,1-Bis(t-butylperoxy)cyclohexane; available under the trade name
"Perhexa C-40" from NOF Corporation. [0171] Zinc oxide: Available
from Sakai Chemical Industry Co., Ltd. [0172] Zinc stearate:
Available under the trade name "Zinc Stearate G" from NOF
Corporation. [0173] Barium sulfate: Available under the trade name
"Precipitated Barium Sulfate 100" from Sakai Chemical Industry Co.,
Ltd. [0174] Calcium carbonate: Available under the trade name
"Silver W" from Shiraishi Calcium Kaisha, Ltd. [0175] Antioxidant:
Available under the trade name "Nocrac NS-6" from Ouchi Shinko
Chemical Industry Co., Ltd.
[0176] 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 by an
inner cover layer and an outer cover layer of given
thicknesses.
TABLE-US-00002 TABLE 2 1 2 3 4 Formulation4 Himilan 1557 42.5 50
(parts by weight) Himilan 1601 42.5 50 Himilan 1605 69 Nucrel
AN4318 15 Nucrel AN4319 84 Nucrel 1560 1 Dynaron 6100P 15 31
Titanium oxide 4.8 2.8 Calcium hydroxide 2.3 Polytail H 2 Behenic
acid 18 Magnesium oxide 1 Magnesium stearate 59
[0177] Trade names of the materials in the table are as follows.
[0178] Himilan: Ionomeric resins available from DuPont-Mitsui
Polychemicals Co., Ltd. [0179] Nucrel AN4318, AN4319: Terpolymers
available from DuPont-Mitsui Polychemicals Co., Ltd. [0180] Nucrel
1560: A copolymer available from DuPont-Mitsui Polychemicals Co.,
Ltd. [0181] Dynaron 6100P: A hydrogenated polymer available from
JSR Corporation. [0182] Titanium oxide: Available under the trade
name "Tipaque R550" from Ishihara Sangyo Kaisha, Ltd. [0183]
Calcium hydroxide: Available under the trade name "CLS-B" from
Shiraishi Calcium Kaisha, Ltd. [0184] Polytail H: A
low-molecular-weight polyolefin polyol available from Mitsubishi
Chemical Corporation. [0185] Behenic acid: Available under the
trade name "NAA-222S" from NOF Corporation. [0186] Magnesium oxide:
Available as "Kyowamag MF150" from Kyowa Chemical Industry Co.,
Ltd. [0187] Magnesium stearate: Available under the trade name
"Magnesium Stearate G" from NOF Corporation.
[0188] Numerous dimples were formed on the surface of the cover
simultaneous with injection molding 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.
[0189] With regard to the dimple patterns in the tables, the dimple
pattern for Examples 1, 3 and 5 is shown in Table 3 (FIG. 3), the
pattern for Examples 2 and 4 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 Number Edge Examples 1, 3 and 5 of Diameter
Depth Volume angle Dimple types dimples (mm) (mm) (mm.sup.3)
(.degree.) Da-I 40 4.1 0.21 1.53 14.0 Da-II 184 3.9 0.20 1.31 14.0
Db-I 96 3.3 0.16 0.73 14.2 Da-III 32 4.1 0.23 1.72 15.6 Da-IV 16
3.9 0.22 1.45 15.4 Db-II 16 3.2 0.15 0.62 13.5 Db-III 8 3.2 0.14
0.49 11.3
TABLE-US-00004 TABLE 4 Number Edge Examples 2 and 4 of Diameter
Depth Volume angle Dimple types dimples (mm) (mm) (mm.sup.3)
(.degree.) Da-I 24 4.5 0.20 1.66 12.3 Da-II 150 4.3 0.19 1.48 12.0
Da-III 66 3.7 0.18 1.02 12.3 Db-I 18 2.7 0.13 0.41 12.4 Db-II 6 2.5
0.12 0.31 12.2 Da-IV 48 4.3 0.19 1.56 13.7 Da-V 12 3.8 0.18 1.15
14.6 Db-III 6 3.4 0.16 0.75 11.8 Db-IV 6 3.3 0.15 0.66 11.4
TABLE-US-00005 TABLE 5 Comparative Examples Number Edge 1 and 5 of
Diameter Depth Volume angle Dimple types dimples (mm) (mm)
(mm.sup.3) (.degree.) Da-I 24 4.7 0.15 1.25 9.8 Da-II 168 4.5 0.15
1.15 9.4 Da-III 48 3.9 0.15 0.85 10.3 Db-I 12 2.9 0.15 0.44 13.3
Db-II 12 2.6 0.11 0.24 11.6 Da-IV 30 4.4 0.16 1.20 10.2 Da-V 36 3.9
0.17 0.94 11.3 Db-III 8 3.5 0.16 0.70 11.8 Db-IV 6 3.4 0.15 0.61
11.4
TABLE-US-00006 TABLE 6 Number Edge Comparative Example 2 of
Diameter Depth Volume angle Dimple types dimples (mm) (mm)
(mm.sup.3) (.degree.) Da-I 12 4.6 0.16 1.28 10.0 Da-II 222 4.4 0.16
1.16 9.9 Da-III 36 3.8 0.15 0.80 10.4 Db-I 12 2.6 0.12 0.58 12.0
Da-IV 12 4.4 0.17 0.25 10.6 Da-V 24 3.8 0.16 1.25 11.0 Db-II 6 3.5
0.16 0.86 11.8 Db-III 6 3.4 0.15 0.70 11.4
TABLE-US-00007 TABLE 7 Number Edge Comparative Example 3 of
Diameter Depth Volume angle Dimple types dimples (mm) (mm)
(mm.sup.3) (.degree.) Da-I 228 4.3 0.17 1.06 11.5 Da-II 36 3.7 0.16
0.74 11.0 Db-I 12 2.5 0.12 0.23 12.2 Db-II 12 3.4 0.17 0.72 12.6
Da-III 42 4.3 0.18 1.14 12.2 Da-IV 24 3.7 0.17 0.80 11.8 Da-V 12
4.3 0.17 1.05 10.6 Da-VI 2 3.9 0.16 0.89 10.5
TABLE-US-00008 TABLE 8 Number Edge Comparative Example 4 of
Diameter Depth Volume angle Dimple types dimples (mm) (mm)
(mm.sup.3) (.degree.) Db-I 114 3.65 0.20 1.07 13.3 Da-I 114 4.0
0.15 1.01 10.4 Db-II 60 3.65 0.20 1.07 13.3 Db-III 12 2.5 0.17 0.43
16.1 Da-II 60 4.0 0.15 1.01 10.4
[0190] Various properties of the resulting multi-piece solid golf
balls were investigated as described below. The results are shown
in Tables 9 and 10.
Center Hardness of Solid Core, Cross-Sectional Hardness Midway
Between Center and Surface of Core, and Surface Hardness of
Core
[0191] The cross-sectional hardness (Shore D hardness) of the solid
core was measured by cutting the core through the center, and
perpendicularly pressing the indenter of a type D durometer
conforming with ASTM D2240-95 against the center of the
cross-section, and at a position midway between the center and
surface of the cross-section.
[0192] The surface hardness (Shore D hardness) of the solid core
was measured by perpendicularly pressing the indenter of a type D
durometer conforming with ASTM D2240-95 against the spherical
surface of the core.
[0193] The above hardnesses are each measured values obtained after
holding the core isothermally at 23.degree. C.
Deflection of Solid Core, Inner Cover Layer-Encased Sphere, and
Ball
[0194] The solid core, inner cover layer-encased sphere and ball
were placed on a hard plate, and the amount of deflection by each
when compressed under a final load of 1,275 N (130 kgf) from an
initial load state of 98 N (10 kgf) was measured. In addition, the
deflection by the ball when compressed under a final load of 5,880
N (600 kgf) from an initial load state of 98 N (10 kgf) was
similarly measured.
[0195] The above deflections are each measured values obtained
after holding the specimen to be measured isothermally at
23.degree. C.
Cover Hardness (Shore D Hardness)
[0196] 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
[0197] 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
[0198] 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
[0199] A driver (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.
[0200] The flight performance was rated according to the following
criteria. [0201] Good: The difference in total distance between
shots taken at a head speed of 54 m/s and shots taken at a head
speed of 35 m/s was less than 97 m [0202] NG: The difference in
total distance between shots taken at a head speed of 54 m/s and
shots taken at a head speed of 35 m/s was 97 m or more
TABLE-US-00009 [0202] TABLE 9 Example 1 2 3 4 5 Core Formulation A
A B C D Diameter (mm) 36.1 36.1 37.3 36.1 37.3 10-130 kgf
deflection (mm) 4.2 4.2 3.4 4.3 3.5 Center hardness Hc (Shore D) 36
36 41 34 37 Cross-sectional hardness Hm midway 41 41 46 38 41
between center and surface (Shore D) Surface hardness Hs (Shore D)
51 51 56 55 59 Inner cover Material 1 1 2 1 2 layer Material
hardness (Shore D) 49 49 56 49 56 Thickness (mm) 1.95 1.95 1.35
1.95 1.35 Inner cover 10-130 kgf deflection (mm) 3.7 3.7 3.0 3.7
3.0 layer-encased sphere Outer cover Material 3 3 4 3 4 layer
Material hardness (Shore D) 57 57 61 57 61 Thickness (mm) 1.35 1.35
1.35 1.35 1.35 Dimples Number of dimple types 7 types 9 types 7
types 9 types 7 types Number of dimples 392 336 392 336 392 SR
value (%) 72 76 72 76 72 VR value (%) 1.20 1.06 1.20 1.06 1.20
Average DP (mm) 0.19 0.18 0.19 0.18 0.19 Average edge angle
(.degree.) 14.2 12.4 14.2 12.4 14.2 Proportion of dimples having an
98 96 98 96 98 edge angle of 12 to 16.degree. (%) Average DM/DP
19.83 21.95 19.83 21.95 19.83 (Total number of Db dimples)/ 0.44
0.12 0.44 0.12 0.44 (Total number of Da dimples) Volume proportion
of Da dimples (%) 82 96 82 96 82 Low-velocity CL ratio (%) 85 78 85
78 85 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 10-130 kgf deflection (mm) 3.2 3.2 2.6 3.2 2.6
10-600 kgf deflection (mm) 10.2 10.2 8.7 11.1 9.4 Initial velocity
(m/s) 77.3 77.3 76.8 77.3 76.8 Hardness Hm - Hc (Shore D) 5 5 5 4 4
relationship Hs - Hm (Shore D) 10 10 10 17 18 Hs - Hc (Shore D) 15
15 15 21 22 Material hardness of outer cover 8 8 5 8 5 layer -
Material hardness of inner cover layer (Shore D) Hs - Material
hardness of 2 2 0 6 3 inner cover layer (Shore D) Hs - Material
hardness of -6 -6 -5 -2 -2 outer cover layer (Shore D) Deflection
Intermediate layer-encased sphere/Core 0.88 0.88 0.88 0.86 0.86
ratio Ball/Core 0.76 0.76 0.76 0.74 0.74 (600 kgf ball
deflection)/(130 3.2 3.2 3.3 3.5 3.6 kgf ball deflection) Flight
HS, 54 m/s Carry (m) 259.1 263.5 263.1 264.3 264.3 Total distance
(m) 274.0 276.4 276.1 277.2 277.6 HS, 35 m/s Carry (m) 161.9 162.0
163.1 162.3 163.6 Total distance (m) 182.6 180.5 181.6 181.2 182.4
Difference in carry (m) 97.2 101.5 100.0 102.0 100.7 Difference in
total distance (m) 91.4 95.9 94.5 96.0 95.2 Rating good good good
good good
TABLE-US-00010 TABLE 10 Comparative Example 1 2 3 4 5 Core
Formulation E E E E A Diameter (mm) 36.1 36.1 36.1 36.1 36.1 10-130
kgf deflection (mm) 4.2 4.2 4.2 4.2 4.2 Center hardness Hc (Shore
D) 36 36 36 36 36 Cross-sectional hardness Hm midway 41 41 41 41 41
between center and surface (Shore D) Surface hardness Hs (Shore D)
51 51 51 51 51 Inner cover Material 1 1 1 1 1 layer Material
hardness (Shore D) 49 49 49 49 49 Thickness (mm) 1.95 1.95 1.95
1.95 1.95 Inner cover 10-130 kgf deflection (mm) 3.7 3.7 3.7 3.7
3.7 layer-encased sphere Outer cover Material 3 3 3 3 3 layer
Material hardness (Shore D) 57 57 57 57 57 Thickness (mm) 1.35 1.35
1.35 1.35 1.35 Dimples Number of dimple types 9 types 8 types 8
types 5 types 9 types Number of dimples 344 330 368 360 344 SR
value (%) 80 78 76 71 80 VR value (%) 0.90 0.88 0.93 0.90 0.90
Average DP (mm) 0.15 0.15 0.16 0.17 0.15 Average edge angle
(.degree.) 10.1 10.2 11.6 12.0 10.1 Proportion of dimples having an
3 4 18 52 3 edge angle of 12 to 16.degree. (%) Average DM/DP 27.39
24.77 23.17 20.97 27.39 (Total number of Db dimples)/ 0.12 0.078
0.07 1.07 0.12 (Total number of Da dimples) Volume proportion of Da
dimples (%) 95 95 97 48 95 Low-velocity CL ratio (%) 80 78 65 75 80
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 10-130 kgf deflection (mm) 3.2 3.2 3.2 3.2 3.2
10-600 kgf deflection (mm) 10.2 10.2 10.2 10.2 10.2 Initial
velocity (m/s) 76.3 76.3 76.3 76.3 77.3 Hardness Hm - Hc (Shore D)
5 5 5 5 5 relationship Hs - Hm (Shore D) 10 10 10 10 10 Hs - Hc
(Shore D) 15 15 15 15 15 Material hardness of outer cover 8 8 8 8 8
layer - Material hardness of inner cover layer (Shore D) Hs -
Material hardness of 2 2 2 2 2 inner cover layer (Shore D) Hs -
Material hardness of -6 -6 -6 -6 -6 outer cover layer (Shore D)
Deflection Intermediate layer-encased sphere/Core 0.88 0.88 0.88
0.88 0.88 ratio Ball/Core 0.76 0.76 0.76 0.76 0.76 (600 kgf ball
deflection)/(130 3.2 3.2 3.2 3.2 3.2 kgf ball deflection) Flight
HS, 54 m/s Carry (m) 264.2 265.0 263.5 263.2 270.8 Total distance
(m) 275.9 276.1 274.5 274.1 282.6 HS, 35 m/s Carry (m) 157.8 156.8
157.7 157.0 160.9 Total distance (m) 175.4 174.9 176.0 175.5 178.1
Difference in carry (m) 106.4 108.2 105.8 106.2 109.9 Difference in
total distance (m) 100.5 101.2 98.5 98.6 104.5 Rating NG NG NG NG
NG
[0203] 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 5 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 5 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 decrease 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 in the
examples according to the present invention were confirmed to be
golf balls which have a small difference in distance when hit at a
high head speed versus when hit at a low head speed, 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.
* * * * *