U.S. patent application number 17/495086 was filed with the patent office on 2022-06-23 for 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 Atsushi KOMATSU.
Application Number | 20220193493 17/495086 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-23 |
United States Patent
Application |
20220193493 |
Kind Code |
A1 |
KOMATSU; Atsushi |
June 23, 2022 |
GOLF BALL
Abstract
A golf ball of the present invention includes a core and a cover
located outside the core and having a plurality of dimples on a
surface thereof A bottom of each of the dimples has a curved shape
protruding toward an outside of the golf ball. A depth d of a
center protruding portion of the bottom of the dimple is a
perpendicular distance between a line S connecting both ends of an
outer periphery of the dimple and a highest point of the protruding
portion. A volume occupation ratio VR of the dimple is less than
0.75. A relationship between Shore D hardness H of a material of
the cover and the depth d (unit: mm) satisfies the following
Formula 1: (H-83)/(-300)>d (Formula 1).
Inventors: |
KOMATSU; Atsushi;
(Chichibu-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BRIDGESTONE SPORTS CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Appl. No.: |
17/495086 |
Filed: |
October 6, 2021 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 2020 |
JP |
2020-211280 |
Claims
1. A golf ball comprising: a core; and a cover located outside the
core and having a plurality of dimples on a surface thereof,
wherein a bottom of each of the dimples has a curved shape
protruding toward an outside of the golf ball; a depth d of a
center protruding portion of the bottom of the dimple is a
perpendicular distance between a line S connecting both ends of an
outer periphery of the dimple and a highest point of the protruding
portion, a volume occupation ratio VR of the dimple is less than
0.75, and a relationship between Shore D hardness H of a material
of the cover and the depth d (unit: mm) satisfies the following
Formula 1: (H-83)/(-300)>d (Formula 1).
2. The golf ball according to claim 1, wherein the Shore D hardness
of the material of the cover is 50 to 60.
3. The golf ball according to claim 1, further comprising an
intermediate layer between the core and the cover, wherein Shore D
hardness of a material of the intermediate layer is 55 or more.
4. The golf ball according to claim 3, wherein the Shore D hardness
of the material of the intermediate layer is higher than the Shore
D hardness of the material of the cover.
5. The golf ball according to claim 1, further comprising a coating
layer located outside the cover, wherein the coating layer contains
delustering particles, average roughness Ra of a surface of the
coating layer is 0.5 to 1.0, and the volume occupation ratio VR of
the dimple is less than 0.70.
6. The golf ball according to claim 1, wherein the number of
dimples having the depth d satisfying the Formula 1 is 50% or more
of the total number of dimples on a surface of the cover.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This Application claims priority from Japanese Patent
Application No. 2020-211280 filed Dec. 21, 2020, which is
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a golf ball.
[0003] It is well known that when a golf ball is hit, backspin is
applied to the golf ball. If too much backspin is applied in a
driver shot, the ball tends to pop up. Accordingly, in order to
extend a flight distance, it is generally required to reduce the
amount of backspin. In order to reduce the amount of backspin, a
golf ball which can have an increased frictional force with a face
of a driver in a driver shot has been proposed.
[0004] For example, JP 2017-006555 A discloses a golf ball having a
plurality of dimples on a surface thereof, of which the bottom has
a curved shape protruding toward an outside of the golf ball. The
golf ball satisfies a predetermined formula of a relationship among
a deformation amount H of the golf ball when a predetermined load
is applied to the golf ball, a virtual plane area S when no dimple
exists on the surface of the golf ball, and a pressurized area PS
which is an area of the golf ball contacting a plane when a
predetermined load is applied to the golf ball satisfies.
[0005] JP 2017-079905 A discloses a golf ball including a core, a
cover, and at least one intermediate layer therebetween, and
satisfying a value obtained by subtracting the surface hardness of
an intermediate layer-encased sphere from the surface hardness of
the ball, and a value obtained by subtracting the surface hardness
of the core from the surface hardness of the intermediate
layer-encased sphere within predetermined ranges. Hardnesses at a
core center, a position 5 mm from the core center, a position 10 mm
from the core center, a position 15 mm from the core center, and a
core surface, in core hardness distribution are within
predetermined ranges. A value obtained by subtracting the center
hardness of the core from the surface hardness of the core is
within a predetermined range. A relationship V/H between a ball
initial velocity V and a golf ball deflection amount H when a
predetermined load is applied to the golf ball is within a
predetermined range.
[0006] Furthermore, JP 2017-086579 A discloses a golf ball
including a two-layer core including an inner layer and an outer
layer, a cover, at least one intermediate layer between the core
and the cover, and a coating film layer formed on the surface of
the cover. In core hardness distribution, hardness Cc at the center
of the inner layer core, hardness C10 at a position 10 mm from the
center of the inner layer core, hardness Cs at the surface of the
inner layer core, and hardness Css at the surface of the outer
layer core satisfy two predetermined formulae. Furthermore, the
sphere including the core encased by the intermediate layer has
higher surface hardness than that of the ball.
SUMMARY OF THE INVENTION
[0007] Any of the documents of JP 2017-006555 A, JP 2017-079905 A,
and JP 2017-086579 A disclose that a dimple has a bottom with a
curved shape protruding toward the outside of the golf ball. The
present inventors have found that the dimple may not necessarily
contribute to an increase in an actual flight distance even if the
protruding shape causes increased frictional force to cause a
decreased amount of backspin since the protruding shape is
disadvantageous in terms of aerodynamic properties. The frictional
force of the dimple having a protruding bottom with respect to the
golf club is influenced by the material hardness of the cover, but
this is not particularly mentioned in the above documents.
[0008] Then, an object of the present invention is to provide a
golf ball in which a bottom of each of the dimples has a curved
shape protruding toward an outside of the golf ball, which makes it
possible to reliably increase flight distance.
[0009] In order to achieve the object, the present invention is a
golf ball including a core and a cover located outside the core and
having a plurality of dimples on a surface thereof, wherein a
bottom of each of the dimples has a curved shape protruding toward
an outside of the golf ball. A depth d of a center protruding
portion of the bottom of the dimple is a perpendicular distance
between a line S connecting both ends of an outer periphery of the
dimple and a highest point of the protruding portion. A volume
occupation ratio VR of the dimple is less than 0.75. A relationship
between Shore D hardness H of a material of the cover and the depth
d (unit: mm) satisfies the following formula 1:
(H-83)/(-300)>d (Formula 1).
[0010] The Shore D hardness of the material of the cover may be 50
to 60.
[0011] The golf ball may further include an intermediate layer
between the core and the cover. In this case, Shore D hardness of a
material of the intermediate layer may be 55 or more.
[0012] The Shore D hardness of the material of the intermediate
layer may be higher than the Shore D hardness of the material of
the cover.
[0013] The golf ball may further include a coating layer located
outside the cover. In this case, the coating layer may contain
delustering particles; average roughness Ra of a surface of the
coating layer may be 0.5 to 1.0; and the volume occupation ratio VR
of the dimple may be less than 0.70.
[0014] The number of dimples having the depth d satisfying the
formula 1 may be 50% or more of the total number of dimples on a
surface of the cover.
[0015] According to the present invention, when the bottom of the
dimple has a curved shape protruding toward the outside of the golf
ball, the relationship between the depth d of the protruding
portion of the bottom of the dimple and the material hardness of
the cover is specified as in the above-mentioned Formula 1, whereby
the contact area of the golf ball with a club face in full shots
(shots using a driver to a middle iron) can be increased, which
makes it possible to reduce the amount of backspin. Furthermore,
the curved protruding shape of the bottom of the dimple is
disadvantageous in terms of aerodynamic properties. Only reduction
in the amount of backspin makes it impossible to achieve an
increase in the flight distance of the golf ball, but the volume
occupation ratio VR of the dimple is reduced to be less than 0.75
to raise the trajectory of the golf ball, whereby increase in the
flight distance can be achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a perspective view which illustrates an embodiment
of a golf ball according to the present invention;
[0017] FIG. 2 is an enlarged cross-sectional view of one dimple of
the golf ball illustrated in FIG. 1;
[0018] FIG. 3 is a perspective view which illustrates another
embodiment of the golf ball according to the present invention;
[0019] FIG. 4 is an enlarged cross-sectional view of one dimple of
the golf ball illustrated in FIG. 3; and
[0020] FIG. 5 is a perspective view which illustrates yet another
embodiment of the golf ball according to the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0021] Embodiments of a golf ball according to the present
invention will be described below with reference to attached
drawings. However, the present invention is not limited
thereto.
[0022] The golf ball according to the present invention includes,
as an embodiment thereof, a core (not shown) and a cover located
outside the core and having a plurality of dimples 10 on a surface
thereof, as illustrated in FIG. 1. A portion of the surface of the
golf ball 1 located among the plurality of dimples 10 is usually
referred to as a land portion 20. The land portion 20 constitutes
the spherical surface of the golf ball 1. Accordingly, the land
portion 20 has a surface with curvature.
[0023] The planar shape of the dimple 10 formed on the surface of
the golf ball 1 (i.e., the shape recognized when an outer periphery
12 of the dimple 10 or a boundary between the dimple 10 and the
land portion 20 is viewed from immediately above the dimple) may be
circular, polygonal, noncircular, and the like. In the present
embodiment, the planar shape is circular. In the case of the
circular shape, the diameter of the dimple is preferably in a range
of 2 to 5 mm. FIG. 5 illustrates an example of a configuration in
which the planar shape of the dimple is noncircular. The dimple
illustrated in FIG. 5 has a planar shape including a combination of
a plurality of curved portions (the number of the curved portions
is 12 in the drawing) protruding toward an inside of the
dimple.
[0024] The dimple 10 of the present embodiment has a shape in which
a part of the bottom thereof is curved so as to protrude toward an
outside of the ball. FIG. 2 illustrates a cross-sectional view of
the dimple 10 along the diameter thereof. As illustrated in FIG. 2,
the dimple 10 has a bottom 14 with a curved shape formed from one
end to the other end of the outer periphery 12. The bottom 14
includes a portion with a curved shape protruding toward the
outside of the ball in a center region, i.e., a center protruding
portion 15, and a portion with a curved shape recessed from the
outside of the ball in a ring-like region in its outer
periphery.
[0025] The bottom 14 is curved so that the depth thereof becomes
the largest at a deepest point 18 located on both sides of the
center protruding portion 15. The location of the deepest point 18
on the plane is preferably in a range of 20 to 45, more preferably
in a range of 25 to 40, and still more preferably in a range of 30
to 35, with a distance between the outer periphery 12 and a center
point 16 of the dimple as 100.
[0026] A depth d of the center protruding portion 15 of the dimple
10 is a perpendicular distance between a line S connecting both
ends of the outer periphery 12 of the dimple and a highest point of
the center protruding portion 15 (center point 16). A relationship
between the depth d (unit: mm) of the center protruding portion 15
and Shore D hardness H of a material which forms a cover, to be
described later, satisfies the following formula 1:
(H-83)/(-300)>d (Formula 1).
[0027] That is, if the depth d is greater than the value of
(H-83)/(-300), the contact area of the golf ball with a face of the
golf club is not sufficient, whereby frictional force cannot be
increased. The value of (H-83)/(-300)-d is preferably 0.002 or
more, and more preferably 0.005 or more. The depth d providing such
a value makes it possible to reliably provide an excellent
frictional force depending on the material hardness of the cover.
The upper limit of the value of (H-83)/(-300)-d is not particularly
limited, and it is preferably 0.010 or less, and more preferably
0.008 or less.
[0028] The depth D of the dimple 10A differs according to the depth
d of the center protruding portion 25. For example, the depth D of
the dimple 10A is greater than the depth d of the center protruding
portion 25, preferably by 0.025 mm or more, and more preferably by
0.030 mm or more. The upper limit of the depth D of the dimple 10A
is not particularly limited, and it is preferably 0.200 mm or less,
and more preferably 0.150 mm or less.
[0029] For the curved shape of the bottom 24 of the dimple 10A, the
lower limit of an edge angle A2 to the center protruding portion is
preferably 2.degree. or more, and more preferably 3.degree. or
more. The upper limit of the edge angle A2 is preferably 15.degree.
or less, and more preferably 11.degree. or less. The edge angle A2
is an angle formed between a tangent line passing through a point
deeper than the depth d on the bottom curve by 10% and the line S
mentioned above.
[0030] It is not necessary for all the dimples formed on the
surface of the golf ball to have the center-protruding shape
described above. Preferably 50% or more, more preferably 70% or
more, still more preferably 80% or more, and most preferably 90% or
more of all the dimples have the center-protruding shape. Of
course, all the dimples may have the center-protruding shape. From
the viewpoint of exerting excellent aerodynamic isotropy and air
resistance, it is preferable that the dimples having the
center-protruding shape described above are uniformly arranged over
the entire surface of the golf ball.
[0031] The upper limit of the total number of the dimples is, but
not limited to, preferably 500 or less, and more preferably 450 or
less. The lower limit of the total number of the dimples is, but is
not limited to, preferably 250 or more, and more preferably 300 or
more.
[0032] A volume occupation ratio VR of the dimples (i.e., ratio of
total volume of the dimples formed in a portion downward from the
plane surrounded by the edge of the dimple in relation to a virtual
spherical volume of the golf ball obtained supposing that no dimple
exists on the surface of the golf ball) is less than 0.75%. The
dimples having the center-protruding shape described above are
disadvantageous in terms of aerodynamic properties. Therefore, the
volume occupation ratio VR of the dimple is set to be less than
0.75% to raise the trajectory of the golf ball, whereby the flight
distance can be increased. The volume occupation ratio VR of the
dimple is preferably 0.73% or less, and more preferably 0.70% or
less. The lower limit of the volume occupation ratio VR of the
dimple is not particularly limited, and is, for example, preferably
0.65% or more, and more preferably 0.68% or more.
[0033] A surface occupation ratio SR of the dimples (i.e., a ratio
of the total area occupied by the dimples to the entire surface
area of a virtual spherical surface of the golf ball obtained by
supposing that no dimples exist on the surface of the golf ball) is
preferably 70% or more, more preferably 75% or more, and still more
preferably 80% or more. The upper limit of the surface occupation
ratio SR of the dimples is not particularly limited, and is
preferably 99% or less. It is particularly preferable that at least
three types of dimples with different sizes be arranged. This makes
it possible to uniformly arrange the dimples on the spherical
surface of the golf ball without a gap.
[0034] A material which forms the cover includes an ionomer resin,
a polyurethane-based thermoplastic elastomer, a thermosetting
polyurethane, and a mixture thereof, but the material is not
limited thereto. In the cover, the abovementioned main component
can be blended with other thermoplastic elastomers, polyisocyanate
compounds, fatty acids or derivatives thereof, basic inorganic
metal compounds, and fillers and the like.
[0035] The Shore D hardness H of the material which forms the cover
satisfies formula 1 as described above. Therefore, the Shore D
hardness H of the material which forms the cover is dependent on
the depth d of the center protruding portion of the dimple, and is,
for example, preferably 50 or more, and more preferably 53 or more.
The Shore D hardness H of the material which forms the cover is
preferably 65 or less, more preferably 62 or less, and still more
preferably 60 or less. Such numerical value ranges can provide an
appropriate amount of spin in shots using a driver to a middle
iron.
[0036] The lower limit of the thickness of the cover is preferably
0.2 mm or more, and more preferably 0.4 mm or more, but the
thickness of the cover is not limited thereto. The upper limit of
the thickness of the cover is preferably 4 mm or less, more
preferably 3 mm or less, and still more preferably 2 mm or
less.
[0037] The core can be formed from a rubber composition containing
rubber as a main component. As this rubber (base rubber) serving as
the main component, synthetic rubber and natural rubber can be
widely used; and examples of the rubber which can be used include
polybutadiene rubber (BR), styrene butadiene rubber (SBR), natural
rubber (NR), polyisoprene rubber (IR), polyurethane rubber (PU),
butyl rubber (IIR), vinyl polybutadiene rubber (VBR), ethylene
propylene rubber (EPDM), nitrile rubber (NBR) and silicone rubber,
but the rubber is not limited thereto. As the polybutadiene rubber
(BR), for example, 1,2-polybutadiene or cis-1,4-polybutadiene or
the like can be used.
[0038] In the core, the rubber composition can be optionally
blended with, for example, a co-crosslinker, a crosslinking
initiator, a filler, an anti-aging agent, an isomerizing agent, a
peptizing agent, sulfur and an organic sulfur compound, in addition
to the abovementioned base rubber. In place of the rubber, a resin
may be used as the main component, and for example, a thermoplastic
elastomer, an ionomer resin, or a mixture thereof can also be
used.
[0039] Preferable examples of the co-crosslinker to be used include
.alpha.,.beta.-unsaturated carboxylic acid or a metal salt thereof,
but the co-crosslinker is not limited thereto. Examples of the
.alpha.,.beta.-unsaturated carboxylic acid or the metal salt
thereof include: acrylic acid and methacrylic acid; and zinc salts,
magnesium salts and calcium salts thereof. The blending ratio of
the co-crosslinker is, but is not limited to, for example,
preferably approximately 5 parts by weight or more, and more
preferably approximately 10 parts by weight or more, with respect
to 100 parts by weight of the base rubber. The blending ratio of
the co-crosslinker is preferably approximately 70 parts by weight
or less, and more preferably approximately 50 parts by weight or
less.
[0040] As the crosslinking initiator, an organic peroxide is
preferably used, and examples thereof include dicumyl peroxide,
t-butyl peroxybenzoate, di-t-butyl peroxide, and
1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, but the
crosslinking initiator is not limited thereto. The blending ratio
of the crosslinking initiator is, but is not limited to, preferably
approximately 0.10 parts by weight or more, more preferably
approximately 0.15 parts by weight or more, and still more
preferably approximately 0.30 parts by weight or more, with respect
to 100 parts by weight of the base rubber. The blending ratio of
the crosslinking initiator is preferably approximately 8 parts by
weight or less, and more preferably approximately 6 parts by weight
or less.
[0041] Examples of the filler which can be used include silver,
gold, cobalt, chromium, copper, iron, germanium, manganese,
molybdenum, nickel, lead, platinum, tin, titanium, tungsten, zinc,
zirconium, barium sulfate, zinc oxide and manganese oxide, but the
filler is not limited thereto. The filler is preferably in the form
of a powder. The blending ratio of the filler is, but is not
limited to, for example, preferably approximately 1 part by weight
or more, more preferably approximately 2 parts by weight or more,
and still more preferably approximately 3 parts by weight or more,
with respect to 100 parts by weight of the base rubber. The
blending ratio of the filler is preferably approximately 100 parts
by weight or less, more preferably approximately 80 parts by weight
or less, and still more preferably approximately 70 parts by weight
or less.
[0042] Examples of the anti-aging agent which can be used include
commercialized products such as NOCRAC NS-6 (manufactured by Ouchi
Shinko Chemical Industrial Co., Ltd.), but the anti-aging agent is
not limited thereto. The blending ratio of the anti-aging agent is,
but is not limited to, preferably approximately 0.1 parts by weight
or more, and more preferably approximately 0.15 parts by weight or
more, with respect to 100 parts by weight of the base rubber. The
blending ratio of the anti-aging agent is preferably approximately
1.0 part by mass or less, and more preferably approximately 0.7
parts by mass or less.
[0043] The resilience of the core 40 can be improved by the
addition of an organic sulfur compound (peptizer). The organic
sulfur compound is selected from thiophenols, thiocarboxylic acids,
and metal salts thereof. Examples of the thiophenols and the
thiocarboxylic acids include thiophenols such as
pentachlorothiophenol, 4-t-butyl-o-thiophenol, 4-t-butylthiophenol
and 2-benzamidothiophenol, and thiocarboxylic acids such as
thiobenzoic acid. As the metal salts thereof, zinc salts and the
like are preferable. The blending ratio of the organic sulfur
compound is preferably approximately 0.5 parts by weight or more,
and more preferably approximately 1 part by weight or more, with
respect to 100 parts by weight of the base rubber, but the ratio is
not limited thereto. The blending ratio of the organic sulfur
compound is preferably approximately 3 parts by weight or less, and
more preferably approximately 2 parts by weight or less.
[0044] The upper limit of the Shore D hardness of the material
which forms the core is preferably 60 or less, more preferably 50
or less, and still more preferably 40 or less. In addition, the
lower limit of the Shore D hardness of the material which forms the
core is preferably 20 or more, and more preferably 30 or more, but
the lower limit is not limited thereto. With the material hardness
of the core in such a range, the feeling of a hit of the golf ball
can be improved.
[0045] The lower limit of the thickness of the core may be 4.5 mm
or more in order to impart a predetermined repulsive force to the
golf ball, and is more preferably 10 mm or more. In addition, the
upper limit of the thickness of the core is, but is not limited to,
preferably 25 mm or less, and more preferably 20 mm or less. The
core is not limited to a core formed of a single layer, and for
example, the core may be formed of a plurality of layers. In this
case, it is preferable that the hardness of each layer of the core
be controlled so as to increase from the inside to the outside of
the golf ball.
[0046] An intermediate layer (not shown) may be optionally provided
between the core and the cover. The intermediate layer is provided
and can provide an appropriate amount of spin in shots using a
driver to a middle iron.
[0047] A material which is preferably used as the main material of
the intermediate layer is the following heated mixture, but the
material is not limited thereto. This material is used for the
intermediate layer, whereby the amount of spin can be decreased at
the time of hitting, and a long flight distance can be obtained.
The mixture contains: a base resin in which (a) a binary random
copolymer of olefin-unsaturated carboxylic acid, and/or a metal ion
neutralized product of a binary random copolymer of
olefin-unsaturated carboxylic acid, and (b) a ternary random
copolymer of olefin-unsaturated carboxylic acid-unsaturated
carboxylic acid ester, and/or a metal ion neutralized product of a
ternary random copolymer of olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester are blended so that the
weight ratio of 100:0 to 0:100 is achieved; (e) a non-ionomeric
thermoplastic elastomer which is blended so that the weight ratio
of 100:0 to 50:50 is achieved with respect to the base resin; (c) 5
to 150 parts by weight of a fatty acid having a molecular weight of
228 to 1500 and/or a derivative thereof, with respect to 100 parts
by weight of a resin component containing the base resin and the
component (e); and (d) 0.1 to 17 parts by weight of a basic
inorganic metal compound which can neutralize an unneutralized acid
group in the base resin and the component (c).
[0048] Here, the "main material" means a material which accounts
for 50% by weight or more, preferably 60% by weight or more, and
still more preferably 70% by weight or more, of the total weight of
the intermediate layer.
[0049] The Shore D hardness of the material which forms the
intermediate layer is preferably 55 or more, and more preferably 57
or more. The Shore D hardness of the material which forms the
intermediate layer is preferably higher than the Shore D hardness
of the material which forms the cover. This can provide an
appropriate amount of spin in shots using a driver to a middle
iron. The upper limit of the Shore D hardness of the material which
forms the intermediate layer is preferably 65 or less, and more
preferably 63 or less, but the upper limit is not limited
thereto.
[0050] The thickness of the intermediate layer is, but is not
limited to, preferably 0.5 mm or more, and more preferably 1 mm or
more. The thickness of the intermediate layer 20 is preferably 10
mm or less, more preferably 5 mm or less, and still more preferably
3 mm or less.
[0051] On the surface of the cover, a coating layer (also referred
to as a painted layer) (not shown) may be optionally provided. The
coating layer is formed of a coating material composition. The
coating material composition may contain delustering particles. The
coating material composition is not particularly limited, and for
example, a urethane-based coating material is preferably used.
Given the need to be capable of enduring the severe use environment
of the golf ball, a two-part curable urethane coating material is
preferable, with the use of a non-yellowing urethane coating
material being particularly preferable.
[0052] In the case of the two-part curable urethane coating
material, it is preferable to use, as the main agent, various
polyols such as saturated polyester polyols, acrylic polyols and
polycarbonate polyols. It is preferable to use, as an isocyanate
which is a curing agent, a non-yellowing polyisocyanate, examples
of which include hexamethylene diisocyanate, isophorone
diisocyanate, and adducts, biurets, isocyanurates, or mixtures
thereof, of hydrogenated xylylene diisocyanate.
[0053] Examples of the delustering particles include silica
particles, melamine particles and acrylic particles. Specific
examples include silica particles, polymethyl methacrylate
particles, polybutyl methacrylate particles, polystyrene particles
and polybutyl acrylate particles. Either organic particles or
inorganic particles may be used, with the use of silica particles
being particularly suitable.
[0054] If such delustering particles are contained in the coating
layer, the aerodynamic performance of the golf ball is
disadvantageous, but in the present embodiment, the volume
occupation ratio VR of the dimple is less than 0.75, to raise the
trajectory, whereby the flight distance can be maintained. When the
delustering particles are contained in the coating layer, the
volume occupation ratio VR of the dimple may be less than 0.70.
Thereby, the trajectory of the golf ball is further raised, whereby
the flight distance can be increased.
[0055] In terms of the light-quenching properties and the coating
properties, the delustering particles have a BET specific surface
area, which is preferably 200 to 400 m.sup.2/g, and more preferably
250 to 350 m.sup.2/g. In terms of the spin performance and the
light-quenching properties, the delustering particles have an
average primary particle size which is preferably 1.0 to 3.0 .mu.m,
and more preferably 2.0 to 2.8 .mu.m. When the average primary
particle size is more than 3.0 .mu.m, the ball surface becomes
rough, which may have an adverse effect on the spin performance of
the golf ball, reducing the spin performance. In addition, when the
average primary particle size is too small, the light-quenching
effect may diminish.
[0056] The blending amount of the delustering particles per 100
parts by mass of the main agent (the total amount of resin
components and solvent) in the coating material composition of the
coating layer may be set to be preferably 5 to 10 parts by mass.
When this blending amount is too high, the viscosity of the coating
material composition increases and the coating operation tends to
be poor. When it is too low, the light-quenching effect may
diminish. The coating layer has average surface roughness Ra which,
from the standpoint of both the amount of spin of the ball on
approach shots and the light-quenching properties, is suitably 0.5
to 1.0. The surface roughness Ra of the coating film means the
arithmetic average roughness in JIS B0601 (1994).
[0057] The shape of the dimple of the golf ball of the present
embodiment has been described with reference to FIGS. 1 and 2, but
the present invention is not limited to a dimple having such a
shape. For example, a dimple having a shape illustrated in another
embodiment illustrated in FIGS. 3 and 4 may be used. Hereinafter,
the other embodiment will be described.
[0058] As illustrated in FIG. 3, on the surface of a golf ball 1, a
plurality of dimples 10A are formed. In the dimple 10A, the bottom
thereof has a curved shape protruding toward the outside of the
ball in the center of the dimple, as illustrated in FIG. 4.
However, as illustrated in FIG. 2, the bottom is not entirely
curved and the leading edge portion has a planar shape.
[0059] More specifically, a bottom 24 shaped from one end of an
outer periphery 22 of the dimple 10A to the other end has a portion
with a curved shape protruding toward the outside of the ball in a
center region thereof and a flat shape in a further central portion
thereof, i.e., a center protruding portion 25, and a portion with a
curved shape recessed from the outside of the ball in a ring-like
region in its outer periphery.
[0060] In the flat region of the center protruding portion 25, a
distance W between both ends 27 is preferably in a range of 35 to
65, more preferably in a range of 40 to 60, and still more
preferably in a range of 45 to 55, with a distance between the
outer periphery 22 and a center point 26 of the dimple as 100.
[0061] An outer periphery 29 of the flat region of the center
protruding portion 25 is configured so that a corner portion
thereof is chamfered. The corner portion is chamfered, whereby the
outer periphery 29 can effectively contribute to the increase in
the contact area of the present invention, and as a result, the
spin performance can be improved. The radius of curvature R of the
chamfered corner portion is preferably 0.4 mm or more, and more
preferably 0.5 mm or more. The upper limit of the radius of
curvature R is preferably 2.5 mm or less, and more preferably 2.0
mm or less.
[0062] A depth d of the center protruding portion 25 in the flat
region is constant. The depth d of the center protruding portion 25
is determined on the basis of the line S connecting both ends of
the outer periphery 22 of the dimple as the reference, as described
above. The relationship between the depth d of the center
protruding portion 25 and the Shore D hardness H of the material
which forms the cover satisfies the above formula 1 as with the
embodiment of FIG. 2. The value of (H-83)/(-300)-d is preferably
0.002 or more, and more preferably 0.005 or more. The depth d
providing the value can certainly provide an excellent frictional
force depending on the material hardness of the cover. The upper
limit of the value of (H-83)/(-300)-d is not particularly limited,
and is preferably 0.010 or less, and more preferably 0.008 or
less.
[0063] In regions on both sides of the center protruding portion
25, the bottom of the dimple is curved so that the depth thereof
becomes greatest at deepest point 28. The location of the deepest
point 28 on the plane is preferably in a range of 25 to 55, more
preferably in a range of 30 to 50, and still more preferably in a
range of 35 to 45, with the distance between the outer periphery 22
and the center point 26 of the dimple as 100.
EXAMPLES
[0064] A golf ball having a configuration shown in Example 1 of
Table 1 was produced. Table 3 shows the blending of a core. Table 4
shows the blendings of an intermediate layer and the cover. Table 5
shows the blending of a paint layer. The protruding shape of a
dimple was a shape having a flat region in a center protruding
portion as illustrated in FIG. 4. The dimples were arranged to have
a pattern illustrated in FIG. 5.
TABLE-US-00001 TABLE 1 Examples 1 2 3 4 5 Intermediate Blending A A
A A B layer Material hardness 57 57 57 57 51 Cover Blending C D E C
C Material hardness H 55 59 62 55 55 Paint layer Blending F F F G F
Delustering particles Absent Absent Absent Present Absent Dimples
Number 326 326 326 326 326 VR 0.70 0.70 0.70 0.67 0.70 Protruding
Number 318 318 318 318 318 Depth d 0.085 0.075 0.068 0.085 0.085
[mm] Value of (H-83)/(-300) 0.093 0.080 0.070 0.093 0.093 Value of
(H-83)/(-300)-d 0.008 0.005 0.002 0.008 0.008 Evaluation of Formula
1 Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory
Ratio of protruding dimples [%] 98 98 98 98 98 Amount of spin 2736
2712 2688 2738 2745 (driver) [rpm] Evaluation Good Good Good Good
Good Flight distance (driver) [m] 232.4 233.5 235.2 232.1 232.2
Evaluation Good Good Good Good Good Amount of spin 5093 5221 5324
5131 5630 (middle iron) [rpm] Evaluation Good Good Good Good
Poor
TABLE-US-00002 TABLE 2 Comparative Examples 1 2 3 4 5 Intermediate
Blending A A A A A layer Material hardness 57 57 57 57 57 Cover
Blending C D E C C Material hardness H 55 59 62 55 55 Paint layer
Blending F F F F G Delustering particles Absent Absent Absent
Absent Present Dimples Number 326 326 326 326 326 VR 0.70 0.70 0.70
0.78 0.75 Protruding Number 318 318 318 318 318 Depth d 0.102 0.085
0.080 0.085 0.085 [mm] Value of (H-83)/(-300) 0.093 0.080 0.070
0.093 0.093 Value of (H-83)/(-300)-d -0.009 -0.005 -0.010 0.008
0.008 Evaluation of formula 1 Not Not Not Satisfactory Satisfactory
satisfactory satisfactory satisfactory Ratio of protruding dimples
[%] 98 98 98 98 98 Amount of spin 2806 2784 2748 2741 2742 (driver)
[rpm] Evaluation Bad Bad Poor Good Good Flight distance 230.2 230.5
230.8 228.8 228.5 (driver) [m] Evaluation Bad Bad Bad Bad Bad
Amount of spin 5225 5315 5390 5087 5122 (middle iron) [rpm]
Evaluation Poor Poor Poor Good Good
TABLE-US-00003 TABLE 3 Polybutadiene 100 Acrylic acid zinc 21
Organic peroxide A 0.3 Organic peroxide B 0.3 Anti-aging agent 0.1
Zinc oxide 29.4 Pentachlorothiophenol zinc salt 0.6
[0065] Polybutadiene in Table 3 is "BR01" (trade name) manufactured
by JSR Corporation. Acrylic acid zinc is manufactured by NIPPON
SHOKUBAI CO., LTD. An organic peroxide A is "PERCUMYL D" (trade
name) manufactured by NOF CORPORATION. An organic peroxide B is
"PEROXA 40" (trade name) manufactured by NOF CORPORATION. An
anti-aging agent is 2,2-methylenebis(4-methyl-6-butylphenol) with
"Nocrac NS-6" (trade name) manufactured by OUCHI SHINKO CHEMICAL
INDUSTRIAL CO., LTD. Zinc oxide is "ZINC OXIDE 3 TYPES" (trade
name) manufactured by SAKAI CHEMICAL INDUSTRY CO., LTD. A
pentachlorothiophenol zinc salt is manufactured by Zhejiang Cho
& Fu Chemical Co., Ltd.
TABLE-US-00004 TABLE 4 A B c D E HPF1000 56 100 -- -- -- Himilan
1605 44 -- 50 50 50 AM7329 -- -- -- 15 50 Surlyn 9320 -- -- 50 35
-- Titanium oxide -- -- 4 4 4
[0066] "HPF1000" in Table 4 is an ionomer resin manufactured by THE
DOW CHEMICAL COMPANY. "Himilan 1605" is an ionomer resin
manufactured by DuPont-Mitsui Polychemicals Co., Ltd. "AM7329" is
an ionomer resin manufactured by DuPont-Mitsui Polychemicals Co.,
Ltd. "Surlyn 9320" is an ionomer resin manufactured by THE DOW
CHEMICAL COMPANY.
TABLE-US-00005 TABLE 5 F G Main agent Polyol 29.84 29.84
Delustering 0 9 particles Solvent 70.16 70.16 Curing agent
Isocyanate 42 42 Solvent 58 58
[0067] As a "polyol" of a main agent in Table 5, a polyester polyol
synthesized by the following method was used. First, a reactor
equipped with a reflux condenser, a dropping funnel, a gas inlet
and a thermometer was charged with 140 parts by mass of
trimethylolpropane, 95 parts by mass of ethylene glycol, 157 parts
by mass of adipic acid and 58 parts by mass of
1,4-cyclohexanedimethanol, followed by raising the temperature to
200 to 240.degree. C. while stirring, for heating (reacting) for 5
hours. Then, a polyester polyol was obtained, which had an acid
value of 4, a hydroxyl value of 170 and a weight-average molecular
weight (Mw) of 28,000. As "delustering particles", "Finesil X-35"
manufactured by Maruo Calcium Co., Ltd. was used.
[0068] As an "isocyanate" for a curing agent, Duranate TPA-100
(trade name) manufactured by Asahi Kasei Corporation as a nurate
body (isocyanurate body) of hexamethylene diisocyanate (HMDI) (NCO
content: 23.1%, non-volatile content: 100%) was used. Butyl acetate
was used as a solvent for both a main agent and a curing agent. The
two-part curable urethane coating material having the above
blending was applied with an air spray gun onto the surface of a
cover on which dimples had been formed, to form a paint layer.
[0069] The golf ball of Example 1 having such a configuration was
subjected to tests to evaluate the amount of spin and flight
distance of the golf ball. First, a driver club ("TourB XD-5" (W#
1) (loft angle:)9.5.degree. manufactured by Bridgestone Sports Co.,
Ltd.) was mounted to a golf ball hitting robot, and a golf ball as
a sample was hit at a head speed of 45 m/s to measure the amount of
backspin and the flight distance. A middle iron club ("TourB X-CB"
(I# 6) manufactured by Bridgestone Sports Co., Ltd.) was mounted to
a golf ball hitting robot, and a golf ball as a sample was hit at a
head speed of 42 m/s to measure the amount of backspin. The results
are shown in Table 1.
[0070] For comparison, golf balls having configurations of
Comparative Examples 2 to 4 shown in Table 2 were produced. The
golf balls were subjected to tests to evaluate the amounts of spin
and flight distances of the golf balls in the same manner as in
Example 1.
[0071] As shown in Table 1, the golf ball of Example 1 having a
dimple volume occupation ratio VR of less than 0.75 and satisfying
the condition of (H-83)/(-300) >d of formula 1 had a less amount
of backspin in a driver shot than that of Comparative Examples 2
and 3 not satisfying the condition of Formula 1, which could have
an increased flight distance. The golf ball of Example 1 also had a
less amount of backspin in the middle iron than that of Comparative
Examples 2 and 3. This is also considered to make it possible to
increase the flight distance using the middle iron.
[0072] Furthermore, the golf ball of Example 1 had substantially
the same amount of backspin in the driver shot as that of
Comparative Example 4 satisfying the condition of formula 1 and
having a dimple volume occupation ratio VR of 0.75 or more, but the
golf ball of Example 1 having a volume occupation ratio VR of 0.70
could have an increased flight distance. The golf ball of Example 1
had substantially the same amount of backspin in the middle iron as
that of Comparative Example 4. This is also considered to make it
possible to increase the flight distance using the middle iron.
[0073] Table 2 shows the golf ball of Comparative Example 1 having
the same material hardness of the cover as that of Example 1 and
not satisfying the condition of formula 1. In a simulation
considering the above test results, in Comparative Example 1, the
depth d of the protruding dimple was too large, as shown in Table
2, whereby the contact area of the golf ball with the club was
small, and the golf ball of Comparative Example 1 had an amount of
backspin more than, and a flight distance less than, those of
Example 1. The golf ball of Comparative Example 1 is also
considered to have a greater amount of backspin using the middle
iron than that in Example 1, which has a decreased flight
distance.
[0074] Table 1 shows the golf balls of Examples 2 and 3 having the
same material hardness of the cover as that of Comparative Examples
2 and 3 and satisfying the conditions of Formula 1. In a simulation
considering the above test results, in Examples 2 and 3, the depth
d of the protruding dimple was smaller than that of Example 1, as
shown in Table 1, whereby the contact area of the golf ball with
the club was large, and the golf balls of Examples 2 and 3 can have
a smaller amount of backspin than that of Example 1, and therefore
can have an increased flight distance. It is considered that the
golf balls of Examples 2 and 3 can have a smaller amount of
backspin using the middle iron than that in Comparative Examples 2
and 3, which can have an increased flight distance.
[0075] Furthermore, as shown in Table 1, the golf ball of Example 4
having almost the same configuration as that of Example 1 except
that delustering particles were blended with a paint layer was
produced, and subjected to tests to evaluate the amount of spin and
the flight distance as with Example 1. For comparison, as shown in
Table 2, the golf ball of Comparative Example 5 satisfying the
condition of Formula 1, having a dimple volume occupation ratio VR
of 0.75 or more, and including a paint layer blended with
delustering particles was produced, and similarly subjected to the
tests. As a result, the amounts of backspin using the driver shot
in Example 4 and Comparative Example 5 were almost equal to each
other, but the golf ball of Example 4 having a volume occupation
ratio VR of 0.67 could have an increased flight distance. The
amount of backspin using the middle iron in Example 4 was also
almost equal to that in Comparative Example 5. Therefore, it is
considered that the flight distance using the middle iron can also
be increased.
[0076] Table 1 shows the golf ball of Example 5 having almost the
same configuration as that of Example 1 except that the material
hardness of the intermediate layer is lower than the material
hardness of the cover. In a simulation considering the above test
results, as shown in Table 1, the amount of backspin in the driver
shot in Example 5 is equal to that in Example 1, and the flight
distance can be maintained, but the amount of backspin in the
middle iron was increased. Therefore, the increase in the flight
distance using the middle iron is considered to be poor.
* * * * *