U.S. patent application number 13/716866 was filed with the patent office on 2014-06-19 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 Hideo WATANABE.
Application Number | 20140171221 13/716866 |
Document ID | / |
Family ID | 50931553 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140171221 |
Kind Code |
A1 |
WATANABE; Hideo |
June 19, 2014 |
MULTI-PIECE SOLID GOLF BALL
Abstract
In a multi-piece solid golf ball having a core, at least one
intermediate layer encasing the core and a cover of at least one
layer encasing the intermediate layer, each intermediate layer is
formed primarily of a resin material and each layer of the cover is
formed primarily of an ionomer resin. The intermediate layer has a
Shore D material hardness of not more than 50 and the cover has a
Shore D material hardness greater than 60, the material hardness of
the cover being higher than the material hardness of the
intermediate layer. The intermediate layer and the cover have a
total thickness of not more than 2.2 mm. The cover has a larger
thickness than the intermediate layer, the ratio (a)/(b) of the
cover thickness (a) to the intermediate layer thickness (b) being
at least 1.1 and not more than 2.0.
Inventors: |
WATANABE; Hideo;
(Chichibushi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BRIDGESTONE SPORTS CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Family ID: |
50931553 |
Appl. No.: |
13/716866 |
Filed: |
December 17, 2012 |
Current U.S.
Class: |
473/374 |
Current CPC
Class: |
A63B 37/0064 20130101;
A63B 37/0045 20130101; A63B 37/0048 20130101; A63B 37/0043
20130101; A63B 37/0092 20130101; A63B 37/0021 20130101; A63B
37/0007 20130101; A63B 37/004 20130101; A63B 37/002 20130101; A63B
37/0039 20130101; A63B 37/0033 20130101; A63B 37/0076 20130101;
A63B 37/0018 20130101; A63B 37/0019 20130101; A63B 37/0031
20130101; A63B 37/0009 20130101 |
Class at
Publication: |
473/374 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Claims
1. A multi-piece solid golf ball comprising a core, at least one
intermediate layer encasing the core and a cover of at least one
layer encasing the intermediate layer, wherein each intermediate
layer is formed primarily of a resin material; each layer of the
cover is formed primarily of an ionomer resin; the intermediate
layer has a Shore D material hardness of not more than 50 and the
cover has a Shore D material hardness greater than 60, the material
hardness of the cover being higher than the material hardness of
the intermediate layer; the intermediate layer and the cover have a
combined thickness of not more than 2.2 mm; and the cover has a
larger thickness than the intermediate layer, the ratio (a)/(b) of
the cover thickness (a) to the intermediate layer thickness (b)
being at least 1.1 and not more than 2.0.
2. The multi-piece solid golf ball of claim 1, wherein the ratio
(c)/(a) of the core diameter (c) to the cover thickness (a) is at
least 30 and not more than 40.
3. The multi-piece solid golf ball of claim 1, wherein the ratio
(c)/(b) of the core diameter (c) to the intermediate layer
thickness (b) is at least 41 and not more than 55.
4. The multi-piece solid golf ball of claim 1, wherein the
thickness of the cover is from 0.5 to 1.2 mm.
5. The multi-piece solid golf ball of claim 1, wherein the resin
material forming the intermediate layer has a melt index (MI) of at
least 2 g/10 min and the resin material forming the cover has a
melt index (MI) of at least 5 g/10 min.
6. The multi-piece solid golf ball of claim 1, wherein at least 30
wt % of the total amount of resin material forming the intermediate
layer is a non-ionomeric resin material.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a multi-piece solid golf
ball having a core, an intermediate layer and a cover formed as
successive layers. More specifically, the invention relates to a
multi-piece solid golf ball having an excellent flight performance
which is intended for use by amateur golfers.
[0002] Numerous golf balls with three-piece constructions wherein,
as described below, an intermediate layer is interposed between a
core and a cover and each layer possesses a specific hardness and
thickness have hitherto been disclosed as solid golf balls for
addressing the needs of amateur golfers having relatively low head
speeds of about 35 to 40 m/s when striking the ball with a driver
(W#1). "Amateur golfers" refers herein to players who have lower
head speeds than professionals and other skilled golfers, for whom
the ball tends to rise poorly after being struck, and for whom the
use of drivers having a somewhat large loft is generally regarded
as preferable.
[0003] For example, prior-art disclosures on multiple-piece solid
golf balls having a total cover thickness of 3.0 mm or less include
the following: U.S. Pat. Nos. 7,086,967, 7,270,611, 7,273,424,
7,201,671, 7,288,031, 7,445,566, 7,563,180, 7,270,614 and
7,377,864.
[0004] However, in the foregoing disclosures, there remains room
for improvement in the flight performance as golf balls for amateur
golfers.
SUMMARY OF THE INVENTION
[0005] It is therefore an object of the present invention to
provide a multi-piece solid golf ball which achieves an even better
flight performance when used by amateur golfers.
[0006] As a result of intensive investigations, the inventor has
discovered that, in order to give the amateur golfer a competitive
edge when playing golf, by forming the cover and the intermediate
layer to relatively small thicknesses, optimizing the thickness
ratio therebetween and also conferring the cover and the
intermediate layer with suitable material hardnesses, the distance
traveled by the ball on shots with a driver (W#1) by an amateur
golfer can be increased, in addition to which a good feel having a
suitably soft touch can be obtained on shots with a driver.
[0007] Accordingly, the invention provides the following
multi-piece solid golf balls.
[1] A multi-piece solid golf ball comprising a core, at least one
intermediate layer encasing the core and a cover of at least one
layer encasing the intermediate layer, wherein each intermediate
layer is formed primarily of a resin material; each layer of the
cover is formed primarily of an ionomer resin; the intermediate
layer has a Shore D material hardness of not more than 50 and the
cover has a Shore D material hardness greater than 60, the material
hardness of the cover being higher than the material hardness of
the intermediate layer; the intermediate layer and the cover have a
total thickness of not more than 2.2 mm; and the cover has a larger
thickness than the intermediate layer, the ratio (a)/(b) of the
cover thickness (a) to the intermediate layer thickness (b) being
at least 1.1 and not more than 2.0. [2] The multi-piece solid golf
ball of [1], wherein the ratio (c)/(a) of the core diameter (c) to
the cover thickness (a) is at least 30 and not more than 40. [3]
The multi-piece solid golf ball of [1], wherein the ratio (c)/(b)
of the core diameter (c) to the intermediate layer thickness (b) is
at least 41 and not more than 55. [4] The multi-piece solid golf
ball of [1], wherein the thickness of the cover is from 0.5 to 1.2
mm. [5] The multi-piece solid golf ball of [1], wherein the resin
material forming the intermediate layer has a melt index (MI) of at
least 2 g/10 min and the resin material forming the cover has a
melt index (MI) of at least 5 g/10 min. [6] The multi-piece solid
golf ball of [1], wherein at least 30 wt % of the total amount of
resin material forming the intermediate layer is a non-ionomeric
resin material.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0008] FIG. 1 is a schematic sectional view showing a multi-piece
solid golf ball (three-layer construction) according to the
invention.
[0009] FIG. 2 is a front view of a golf ball showing the dimple
pattern used on the balls in the examples.
DETAILED DESCRIPTION OF THE INVENTION
[0010] The invention is described in greater detail below.
[0011] The multi-piece solid golf ball of the invention, as shown
in FIG. 1, is a golf ball G having a core 1, an intermediate layer
2 encasing the core, and a cover 3 encasing the intermediate layer.
A large number of dimples D are formed on the surface of the cover.
The core 1, the intermediate layer 2 and the cover 3 are not
limited to single layers, and may each be formed of a plurality of
two or more layers.
[0012] In the invention, the core diameter, while not subject to
any particular limitation, is preferably at least 38.3 mm, more
preferably at least 38.5 mm, and even more preferably at least 38.7
mm. The core diameter has no particular upper limit, but is
preferably not more than 40.9 mm, more preferably not more than
40.1 mm, and even more preferably not more than 39.3 mm. At a core
diameter outside of this range, the initial velocity of the ball
may decrease or the feel at impact may worsen.
[0013] The core has a deflection when a load is applied thereto,
i.e., a deflection (mm) when compressed under a final load of
1,275.9 N (130 kgf) from an initial load state of 98.1 N (10 kgf),
which, although not particularly limited, is preferably at least
2.5 mm, more preferably at least 3.0 mm, and even more preferably
at least 3.2 mm. The core deflection has no particular upper limit,
but is preferably not more than 6.0 mm, more preferably not more
than 5.0 mm, and even more preferably not more than 4.2 mm. If this
value is too small, i.e., if the core is too hard, the spin rate
may rise excessively, resulting in a less than satisfactory
distance, and the feel on full shots may be too hard. On the other
hand, if the above value is too large, i.e., if the core is too
soft, the ball rebound may become too small, resulting in a less
than satisfactory distance, and the feel on full shots may be too
soft. Also, the durability to cracking on repeated impact may
worsen.
[0014] The core has a surface hardness, expressed as a JIS-C
hardness value, which, although not subject to any particular
limitation, is preferably at least 70, more preferably at least 75,
and even more preferably at least 80. The JIS-C surface hardness
has no particular upper limit, but is preferably not more than 93,
more preferably not more than 88, and even more preferably not more
than 85. If this value is too low, the spin rate may rise
excessively or the rebound may decrease, resulting in a less than
satisfactory distance. On the other hand, if the above value is too
large, the feel at impact may become hard or the durability to
cracking on repeated impact may worsen.
[0015] The core has a center hardness, expressed as a JIS-C
hardness value, which, although not subject to any particular
limitation, is preferably at least 55, more preferably at least 57,
and even more preferably at least 59. The JIS-C center hardness has
no particular upper limit, but is preferably not more than 68, more
preferably not more than 65, and even more preferably not more than
64. If this value is too low, the durability to cracking on
repeated impact may worsen. On the other hand, if the above value
is too large, the spin rate may rise excessively, resulting in a
less than satisfactory distance.
[0016] The cross-sectional hardness at a position midway between
the surface and the center of the core, expressed as a JIS-C
hardness value, is preferably at least 62, more preferably at least
65, and even more preferably at least 67. The cross-sectional
hardness has no particular upper limit, but is preferably not more
than 81, more preferably not more than 77, and even more preferably
not more than 72. At a cross-sectional hardness outside of this
range, the spin rate may increase, resulting in a poor flight, or
the durability to cracking on repeated impact may worsen.
[0017] It is preferable for the core hardness to increase gradually
from the center to the surface of the core, and for the difference
therebetween to be at least 15 JIS-C hardness units. The hardness
difference is more preferably at least 16, with the upper limit
being preferably not more than 40, and more preferably not more
than 35. If the above hardness difference is too small, the spin
rate-lowering effect on shots with a W#1 may be inadequate, which
may result in a less than satisfactory distance. On the other hand,
if the above hardness difference is too large, the initial velocity
of the ball on actual shots may become lower, resulting in a less
than satisfactory distance, or the durability to cracking on
repeated impact may worsen. It is desirable for the above core
hardness profile to be one having a linear slope from the center
toward the surface.
[0018] In addition, in the core hardness profile, the difference
between the cross-sectional hardness A at a position midway between
the center and the surface of the core and the average B of the
hardnesses at the core center and core surface, i.e., the value
A-B, is preferably .+-.5 or less, more preferably .+-.4 or less,
and even more preferably .+-.3 or less. If this value A-B is too
large, the spin rate-lowering effect on W#1 shots, may be
inadequate, resulting in a less than satisfactory distance.
[0019] The material making up the core having the desired
properties mentioned above is not subject to any particular
limitation, although the core can be formed using a rubber
composition which includes, for example, a co-crosslinking agent,
an organic peroxide, an inert filler and an organosulfur compound.
Polybutadiene is preferably used as the base rubber of such a
rubber composition.
[0020] The polybutadiene has a cis-1,4 bond content on the polymer
chain of typically at least 60 wt %, preferably at least 80 wt %,
more preferably at least 90 wt %, and most preferably at least 95
wt %. Too low a cis-1,4 bond content among the bonds on the
molecule may lead to a lower resilience.
[0021] The polybutadiene has a 1,2-vinyl bond content on the
polymer chain of typically not more than 2%, preferably not more
than 1.7%, and more preferably not more than 1.5%, of the bonds on
the polymer chain. Too high a 1,2-vinyl bond content may lead to a
lower resilience.
[0022] To obtain the rubber composition in a molded and vulcanized
form having a high resilience that increases the distance traveled
by the ball, the polybutadiene used in the invention is preferably
one synthesized with a rare-earth catalyst or a Group VIII metal
compound catalyst. Polybutadiene synthesized with a rare-earth
catalyst is especially preferred.
[0023] Such rare-earth catalysts are not subject to any particular
limitation. Exemplary rare-earth catalysts include those made up of
a combination of a lanthanide series rare-earth compound with an
organoaluminum compound, an alumoxane, a halogen-bearing compound
and an optional Lewis base.
[0024] Examples of suitable lanthanide series rare-earth compounds
include halides, carboxylates, alcoholates, thioalcoholates and
amides of atomic number 57 to 71 metals.
[0025] The use of a neodymium catalyst in which a neodymium
compound serves as the lanthanide series rare-earth compound is
particularly advantageous because it enables a polybutadiene rubber
having a high cis-1,4 bond content and a low 1,2-vinyl bond content
to be obtained at an excellent polymerization activity. Suitable
examples of such rare-earth catalysts include those mentioned in
JP-A 11-35633, JP-A 11-164912 and JP-A 2002-293996.
[0026] To enhance the resilience, it is preferable for the
polybutadiene synthesized using the lanthanide series rare-earth
compound catalyst to account for at least 10 wt %, preferably at
least 20 wt %, and more preferably at least 40 wt %, of the rubber
components.
[0027] Rubber components other than the above-described
polybutadiene may be included in the base rubber insofar as the
objects of the invention are attainable. Illustrative examples of
rubber components other than the above-described polybutadiene
include other polybutadienes and other diene rubbers, such as
styrene-butadiene rubber, natural rubber, isoprene rubber and
ethylene-propylene-diene rubber.
[0028] Examples of co-crosslinking agents include unsaturated
carboxylic acids and the metal salts of unsaturated carboxylic
acids.
[0029] Specific examples of unsaturated carboxylic acids include
acrylic acid, methacrylic acid, maleic acid and fumaric acid.
Acrylic acid and methacrylic acid are especially preferred.
[0030] The metal salts of unsaturated carboxylic acids, while not
subject to any particular limitation, are exemplified by the
above-mentioned unsaturated carboxylic acids neutralized with a
desired metal ion. Specific examples include the zinc and magnesium
salts of methacrylic acid and acrylic acid. The use of zinc
acrylate is especially preferred.
[0031] The unsaturated carboxylic acid and/or metal salt thereof is
included in an amount, per 100 parts by weight of the base rubber,
of generally at least 10 parts by weight, preferably at least 15
parts by weight, and more preferably at least 18 parts by weight,
but generally not more than 60 parts by weight, preferably not more
than 50 parts by weight, more preferably not more than 45 parts by
weight, and most preferably not more than 40 parts by weight. Too
much may make the core too hard, giving the ball an unpleasant feel
on impact, whereas too little may lower the rebound.
[0032] The organic peroxide may be a commercially available
product, suitable examples of which include Percumyl D (produced by
NOF Corporation), Perhexa 3M (NOF Corporation) and Luperco 231XL
(Atochem Co.). These may be used singly, or two or more may be used
together.
[0033] The amount of organic peroxide included per 100 parts by
weight of the base rubber is generally at least 0.1 part by weight,
preferably at least 0.3 part by weight, more preferably at least
0.5 part by weight, and most preferably at least 0.7 part by
weight. The upper limit is generally not more than 5 parts by
weight, preferably not more than 4 parts by weight, more preferably
not more than 3 parts by weight, and most preferably not more than
2 parts by weight. Too much or too little organic peroxide may make
it impossible to achieve a ball having a good feel, durability and
rebound.
[0034] Examples of suitable inert fillers include zinc oxide,
barium sulfate and calcium carbonate. These may be used singly, or
two or more may be used together.
[0035] The amount of inert filler included per 100 parts by weight
of the base rubber is generally at least 1 part by weight, and
preferably at least 5 parts by weight, but generally not more than
100 parts by weight, preferably not more than 80 parts by weight,
and more preferably not more than 60 parts by weight. Too much or
too little inert filler may make it impossible to achieve a proper
weight and a good rebound.
[0036] In addition, an antioxidant may be included if necessary.
Illustrative examples of suitable commercial antioxidants include
Nocrac NS-6 and Nocrac NS-30 (both available from Ouchi Shinko
Chemical Industry Co., Ltd.), and Yoshinox 425 (available from
Yoshitomi Pharmaceutical Industries, Ltd.). These may be used
singly, or two or more may be used together.
[0037] The amount of antioxidant included per 100 parts by weight
of the base rubber is more than 0, preferably at least 0.05 part by
weight, and more preferably at least 0.1 part by weight, but
generally not more than 3 parts by weight, preferably not more than
2 parts by weight, more preferably not more than 1 part by weight,
and most preferably not more than 0.5 part by weight. Too much or
too little antioxidant may make it impossible to achieve a good
rebound and durability.
[0038] An organosulfur compound may be included in the core so as
to enhance the rebound and increase the initial velocity of the
golf ball. It is recommended that thiophenols, thionaphthols,
halogenated thiophenols, or metal salts thereof be included here as
the organosulfur compound. Illustrative examples include
pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol,
p-chlorothiophenol, the zinc salt of pentachlorothiophenol, and
diphenylpolysulfides, dibenzylpolysulfides, dibenzoylpolysulfides,
dibenzothiazoylpolysulfides and dithiobenzoylpolysulfides having 2
to 4 sulfurs. The use of diphenyldisulfide or the zinc salt of
pentachlorothiophenol is especially preferred.
[0039] The amount of the organosulfur compound included per 100
parts by weight of the base rubber is preferably not more than 5
parts by weight, more preferably not more than 3 parts by weight,
and even more preferably not more than 2.5 parts by weight. With
the inclusion of too much organosulfur compound, it may not be
possible to expect a further rebound-improving effect (particularly
on shots with a W#1), the core may become too soft, and the feel
may worsen.
[0040] It is desirable to produce the core by using an ordinary
mixing apparatus such as a Banbury mixer or a roll mill to mix the
core composition containing the above ingredients,
compression-molding or injection-molding the mixed composition
using a core-forming mold, then suitably heating and curing the
molded body at a temperature sufficient for the crosslinking agent
and the co-crosslinking agent to act, generally from about
130.degree. C. to about 170.degree. C., and especially 150 to
160.degree. C., for a period of from 10 to 40 minutes, and
especially 12 to 20 minutes, so as to achieve the intended hardness
profile.
[0041] Next, the intermediate layer is described.
[0042] The intermediate layer has a material hardness, expressed as
a Shore D hardness value (measured with a type D durometer in
accordance with ASTM D2240; the same applies below), of not more
than 50, preferably not more than 45, and more preferably not more
than 40. The intermediate layer material hardness has a lower limit
value, expressed in terms of Shore D hardness, of at least 15, and
preferably at least 25. If the intermediate layer is too soft, the
spin rate on full shots may rise excessively, resulting in a less
than satisfactory distance and the durability to cracking under
repeated impact may worsen. On the other hand, if the intermediate
layer is too hard, the durability to cracking on repeated impact
may worsen, and the spin rate on full shots may rise, resulting in
a less than satisfactory distance. Moreover, in such cases, the
feel at impact may worsen.
[0043] The intermediate layer has a thickness of preferably at
least 0.4 mm, more preferably at least 0.6 mm, and even more
preferably at least 0.8 mm. The upper limit is preferably not more
than 1.0 mm, more preferably not more than 0.95 mm, and even more
preferably not more than 0.9 mm. If the intermediate layer is too
thin, the durability of the ball to cracking on repeated impact may
worsen or the feel at impact may worsen.
[0044] The intermediate layer material is not particularly limited;
various types of thermoplastic resins or thermoplastic elastomers
may be used for this purpose. In particular, the use of
non-ionomeric resin materials such as polyester elastomers,
polyurethanes, styrene-based elastomers and olefin-based elastomers
is preferred. The use of polyester elastomers is most preferred. In
such a case, setting the amount of non-ionomeric resin material to
at least 30 wt % of the total amount of resin material in the
intermediate layer is preferred from the standpoint of increasing
the ball rebound and distance. The amount is more preferably at
least 50 wt %, and even more preferably 100 wt %. At a
non-ionomeric resin material content below the above range, it may
not be possible to obtain an intermediate layer material that is
soft and has a high resilience, and it may not be possible to
achieve an increased distance.
[0045] From the standpoint of, for example, ensuring flow
properties that are particularly suitable for injection molding and
thus improving the moldability, it is preferable to regulate the
melt index of the above intermediate layer material. In this case,
the melt index (MI), as measured in accordance to ASTM D1238 at a
test temperature of 190.degree. C. and a test load of 21.2 N (2.16
kgf), is typically at least 5 g/10 min, preferably at least 7 g/10
min, and more preferably at least 9 g/10 min. It is recommended
that the upper limit be set to preferably not more than 20 g/10
min. If the melt index is too low, molding may be difficult to
carry out or the sphericity of the intermediate layer-covered
sphere may decrease, giving rise to variability in the cover
thickness, which may result in greater variability in the flight of
the ball. On the other hand, if the melt index is too high, the
durability to cracking on repeated impact may worsen.
[0046] Next, the Shore D material hardness of the cover used in the
invention is a value which is greater than 60, preferably at least
62, and more preferably at least 63, but preferably not more than
70, and more preferably not more than 67. If the cover is softer
than the above range, the ball may be too receptive to spin or the
rebound may be inadequate, resulting in a shorter distance, or the
scuff resistance may worsen. On the other hand, if the cover is too
hard, the ball may have a poor durability to cracking on repeated
impact, or may have a poor feel at impact in the short game or when
struck with a putter.
[0047] The cover has a thickness of preferably at least 0.5 mm,
more preferably at least 0.7 mm, and even more preferably at least
0.9 mm, but preferably not more than 1.2 mm, more preferably not
more than 1.15 mm, and even more preferably not more than 1.1 mm.
At a cover thickness greater than the above range, the ball may be
too receptive to spin on shots with a W#1, resulting in a less than
satisfactory distance. On the other hand, if the cover is thinner
than the above range, the ball may have a poor durability to
cracking on repeated impact, or may be too receptive to spin on
shots with a W#1, resulting in a less than satisfactory
distance.
[0048] The cover material is formed primarily of an ionomer resin.
Use can be made of, specifically, an ionomer such as Surlyn
(available from E.I. DuPont de Nemours & Co.), and Himilan and
AM7331 (both from DuPont-Mitsui Polychemicals Co., Ltd.).
[0049] From the standpoint of, for example, ensuring flow
properties that are particularly suitable for injection molding,
and thus a good moldability, it is preferable to regulate the melt
index of the above cover material. In this case, the melt index
(MI), as measured in accordance to ASTM D1238 at a test temperature
of 190.degree. C. and a test load of 21.2 N (2.16 kgf), is
typically at least 2 g/10 min, preferably at least 2.5 g/10 min,
and more preferably at least 3 g/10 min. It is recommended that the
upper limit be set to preferably not more than 10 g/10 min, and
more preferably not more than 5 g/10 min. If the melt index is too
low, molding may be difficult to carry out or the sphericity of the
ball may decrease, which may result in greater variability in the
flight of the ball. On the other hand, if the melt index is too
high, the durability to cracking on repeated impact may worsen.
[0050] In addition to the above resin components, various additives
may be optionally included in the above-described resin materials
for the intermediate layer and the cover. Examples of such
additives include pigments, dispersants, antioxidants, ultraviolet
absorbers, ultraviolet stabilizers, mold release agents,
plasticizers, and inorganic fillers (e.g., zinc oxide, barium
sulfate, titanium dioxide).
Combined Thickness of Intermediate Layer and Cover
[0051] In this invention, the combined thickness of the
intermediate layer and the cover is not more than 2.2 mm,
preferably not more than 2.1 mm, and more preferably not more than
2.0 mm. The lower limit in the combined thickness is preferably at
least 0.9 mm, more preferably at least 1.3 mm, and even more
preferably at least 1.7 mm. If the combined thickness is too large,
the spin rate on full shots will increase, resulting in a less than
satisfactory distance. On the other hand, if the combined thickness
is too small, the spin rate on full shots may increase, resulting
in a less than satisfactory distance and the durability to cracking
on repeated impact may worsen.
Ratio of Cover Thickness to Intermediate Layer Thickness
[0052] In this invention, it is critical for the ratio of the cover
thickness to the intermediate layer thickness to be suitably set
within a given range. Specifically, the ratio (a)/(b) of the cover
thickness (a) to the intermediate layer thickness (b) is at least
1.1, preferably at least 1.15, and more preferably at least 1.2,
with the upper limit being not more than 2.0, preferably not more
than 1.5, and even more preferably not more than 1.4. At a value
outside the above range, a suitable spin rate is not obtained,
resulting in a less than satisfactory distance.
Ratio of Core Diameter to Cover Thickness
[0053] In this invention, although not subject to any particular
limitation, it is preferable for the ratio of the core diameter to
the cover thickness to be suitably set within a given range.
Specifically, the ratio (c)/(a) of the core diameter (c) to the
cover thickness (a) is preferably at least 30, more preferably at
least 32, and even more preferably at least 34, with the upper
limit being preferably not more than 40, more preferably not more
than 38, and even more preferably not more than 36. At a value
outside the above range, a suitable spin rate may not be obtained,
which may result in a less than satisfactory distance.
Ratio of Core Diameter to Intermediate Layer Thickness
[0054] In this invention, although not subject to any particular
limitation, it is preferable for the ratio of the core diameter to
the intermediate layer thickness to be suitably set within a given
range. Specifically, the ratio (c)/(b) of the core diameter (c) to
the intermediate layer thickness (b) is preferably at least 41,
more preferably at least 43, and even more preferably at least 45,
with the upper limit being preferably not more than 55, more
preferably not more than 50, and even more preferably not more than
48. At a value outside the above range, a suitable spin rate may
not be obtained, which may result in a less than satisfactory
distance.
Relationship Between Intermediate Layer Material Hardness and Cover
Material Hardness
[0055] In the present invention, it is critical for the following
relationship between the intermediate layer material hardness and
the cover material hardness to be satisfied:
cover material hardness>intermediate layer material
hardness.
By designing the golf ball in such a way that the material hardness
of the cover is higher than the material hardness of the
intermediate layer, the flight performance can be further enhanced,
enabling a crisp feel at impact to be obtained.
[0056] In the practice of the invention, numerous dimples may be
formed on the surface of the cover. The dimples arranged on the
cover surface, while not subject to any particular limitation,
number preferably at least 280, more preferably at least 300, and
even more preferably at least 320, but preferably not more than
360, more preferably not more than 350, and even more preferably
not more than 320. If the number of dimples is higher than the
above range, the ball will tend to have a low trajectory, which may
shorten the distance of travel. On the other hand, if the number of
dimples is smaller than the above range, the ball will tend to have
a high trajectory, as a result of which an increased distance may
not be achieved.
[0057] The geometric arrangement of the dimples on the ball may be,
for example, octahedral or icosahedral. In addition, the dimple
shapes may be of one, two or more types suitably selected from
among not only circular shapes, but also various polygonal shapes,
such as square, hexagonal, pentagonal and triangular shapes, as
well as dewdrop shapes and oval shapes. The diameter (in polygonal
shapes, the lengths of the diagonals), although not subject to any
particular limitation, is preferably set to from 2.5 to 6.5 mm. In
addition, the depth, although not subject to any particular
limitation, is preferably set to from 0.08 to 0.30 mm.
[0058] The value V.sub.0, defined as the spatial volume of a dimple
below the flat plane circumscribed by the dimple edge, divided by
the volume of the cylinder whose base is the flat plane and whose
height is the maximum depth of the dimple from the base, although
not subject to any particular limitation, may be set to from 0.35
to 0.80 in this invention.
[0059] From the standpoint of reducing aerodynamic resistance, the
ratio SR of the sum of individual dimple surface areas, each
defined by the flat plane circumscribed by the edge of a dimple,
with respect to the surface area of a hypothetical sphere were the
ball surface to have no dimples thereon, although not subject to
any particular limitation, is preferably set to from 60 to 90%.
[0060] The ratio VR of the sum of the spatial volumes of individual
dimples, each formed below the flat plane circumscribed by the edge
of a dimple, with respect to the volume of a hypothetical sphere
were the ball surface to have no dimples thereon, although not
subject to any particular limitation, may be set to from 0.6 to 1%
in this invention.
[0061] In this invention, by setting the above V.sub.0, SR and VR
values in the foregoing ranges, the aerodynamic resistance is
reduced, in addition to which a trajectory which provides a good
distance readily arises, enabling the flight performance to be
enhanced.
[0062] The golf ball of the invention, which can be manufactured so
as to conform with the Rules of Golf for competitive play, is
preferably produced to a ball diameter which is of a size that will
not pass through a ring having an inside diameter of 42.672 mm, but
is not more than 42.80 mm, and to a weight of generally from 45.0
to 45.93 g.
[0063] In the invention, the surface of the golf ball cover may be
subjected to various types of treatment, such as surface
preparation, stamping and painting, in order to enhance the design
and durability of the ball.
[0064] As was explained above, the multi-piece solid golf ball of
the invention further increases the flight performance, enabling
amateur golfers to play golf very competitively. Moreover, a good,
solid feel at impact can be obtained.
EXAMPLES
[0065] Working Examples of the invention and Comparative Examples
are given below by way of illustration, and not by way of
limitation.
Examples 1 to 3, Comparative Examples 1 to 6
[0066] Solid cores were produced by preparing rubber compositions
according to the formulations shown in Table 1 below, then molding
and vulcanizing the compositions at 155.degree. C. for 15
minutes.
TABLE-US-00001 TABLE 1 Core formulation (parts by Example
Comparative Example weight) 1 2 3 1 2 3 4 5 6 Polybutadiene 100 100
100 100 100 100 100 100 100 Zinc acrylate 28.5 26.1 23.7 23.7 23.7
28.5 28.5 28.5 28.5 Peroxide 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2
Antioxidant 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Zinc oxide 20.1
21.1 22.1 17.2 28.1 17.5 19.4 24.2 20.8
[0067] Details on the above core materials are given below. The
numbers in the table represent parts by weight. [0068]
Polybutadiene: Available under the trade name "BR 730" from JSR
Corporation. [0069] Peroxide: A mixture of
1,1-di(t-butylperoxy)cyclohexane and silica, available under the
trade name "Perhexa C-40" from NOF Corporation. [0070] Antioxidant:
2,2-Methylenebis(4-methyl-6-butylphenol), available under the trade
name "Nocrac NS-6" from Ouchi Shinko Chemical Industry Co.,
Ltd.
Formation of Intermediate Layer and Cover
[0071] Next, intermediate layers were formed by injection-molding
resin materials of the compositions shown in Table 2 over the
respective solid cores fabricated as described above, thereby
giving in each Example a sphere composed of a solid core encased by
an intermediate layer (an intermediate layer-covered sphere). Next,
a cover was formed by injection-molding over this sphere a resin
material of the composition shown in Table 2, thereby giving a
multi-piece solid golf ball having a three-layer construction
composed of a solid core encased by an intermediate layer and a
cover. Dimples in the arrangement shown in FIG. 2 were formed at
this time on the surface of the ball cover in each of the Examples
of the invention and the Comparative Examples. Details on the
dimples are given in Table 3.
TABLE-US-00002 TABLE 2 No. 1 No. 2 No. 3 No. 4 No. 5 Surlyn 9945 50
Surlyn 8940 50 Surlyn 8120 100 Himilan 1557 30 Himilan 1855 20
AM7331 50 Hytrel 3046 100 Hytrel 4001 15 T-8260 100 Polyethylene
wax 1.5 Isocyanate compound 9 Titanium oxide 5 3.5 5 2.5 Numbers in
the table indicate parts by weight.
[0072] The above trade names are explained below.
[0073] The trade names of the chief materials mentioned in the
table are as follows. [0074] Surlyn: Ionomers available from E.I.
DuPont de Nemours and Co. [0075] Himilan and AM7331: Ionomers
available from DuPont-Mitsui Polychemicals Co., Ltd. [0076] Hytrel:
Polyester elastomers available from DuPont-Toray Co., Ltd. [0077]
T-8260: A MDI-PTMG type thermoplastic polyurethane available from
DIC Bayer Polymer under the trade name "Pandex" [0078] Polyethylene
wax: Available under the trade name "Sanwax 161P" from Sanyo
Chemical Industries, Ltd. [0079] Isocyanate compound:
4,4'-Diphenylmethane diisocyanate
TABLE-US-00003 [0079] TABLE 3 Number of Diameter Depth No. dimples
(mm) (mm) V.sub.0 SR VR 1 12 4.6 0.15 0.47 81 0.783 2 234 4.4 0.15
0.47 3 60 3.8 0.14 0.47 4 6 3.5 0.13 0.46 5 6 3.4 0.13 0.46 6 12
2.6 0.10 0.46 Total 330
Dimple Definitions
[0080] Diameter: Diameter of flat plane circumscribed by edge of
dimple. [0081] Depth: Maximum depth of dimple from flat plane
circumscribed by edge of dimple. [0082] V.sub.0: Spatial volume of
dimple below flat plane circumscribed by dimple edge, divided by
volume of cylinder whose base is the flat plane and whose height is
the maximum depth of dimple from the base. [0083] SR: Sum of
individual dimple surface areas, each defined by the flat plane
circumscribed by the edge of a dimple, as a percentage of the
surface area of a hypothetical sphere were the ball to have no
dimples on the surface thereof (units: %). [0084] VR: Sum of
spatial volumes of individual dimples formed below flat plane
circumscribed by the edge of a dimple, as a percentage of the
volume of a hypothetical sphere were the ball to have no dimples on
the surface thereof (units: %).
[0085] For each of the golf balls obtained, physical properties
such as the thicknesses and hardnesses of the respective layers,
and also the flight performance and feel at impact of the balls,
were evaluated by the methods described below. The results are
presented in Tables 4 and 5. All of the measurements were carried
out in a 23.9.+-.1.degree. C. atmosphere.
(1) Core Deflection (mm)
[0086] The core or an intermediate layer-covered sphere was
compressed in a 23.9.+-.1.degree. C. atmosphere at a rate of 10
mm/s, and the deflection (mm) upon applying a final load of 1,275.9
N (130 kgf) from an initial load state of 98.1 N (10 kgf) was
measured. In each case, the average of measurements taken on ten
balls (N=10) was determined.
(2) Center Hardness, Surface Hardness and Cross-Sectional Hardness
of Core
[0087] The surface of the core being spherical, the durometer
indenter was set substantially perpendicular to this spherical
surface, and the Shore D hardness was measured with a type D
durometer in accordance with ASTM-2240. The JIS-C hardness was
measured in accordance with JIS K6301-1975.
[0088] The center hardness and the cross-sectional hardness midway
between the core surface and the core center were determined by
cutting the core into two with a fine cutter, and measuring the
hardnesses at specific positions in accordance with the respective
hardness standards.
(3) Material Hardnesses of Intermediate Layer and Cover (Hardnesses
of Sheet-Type Molded Materials)
[0089] The material that forms each layer was molded into a sheet
having a thickness of 2 mm and held for 2 weeks at 23.+-.2.degree.
C., following which the Shore D hardness was measured with a type D
durometer in accordance with ASTM-2240.
(4) Melt Index (MI) Values of Intermediate Layer Material and Cover
Material
[0090] The melt index (MI) values of the materials used to form the
respective layers were measured in accordance with ASTM D1238 (test
temperature, 190.degree. C.; test load, 21.2 N (2.16 kgf)).
(5) Flight Performance on Shots with a Driver
[0091] The distance was measured by mounting a driver (W#1)
manufactured by Bridgestone Sports Co., Ltd. (TourStage ViQ, 2012
model; loft, 11.5.degree.) on a golf swing robot and striking the
ball at a head speed (HS) of 38 m/s. The flight performance was
rated according to the criteria indicated below. In addition, the
spin rate of the ball immediately after being struck in the same
way was measured with an apparatus for measuring initial
conditions. [0092] Good: Total distance was 178 m or more [0093]
NG: Total distance was less than 178 m
(6) Feel
[0094] The feel of the ball when hit with a driver (W#1) by ten
amateur golfers having head speeds (HS) of 35 to 40 m/s was sensory
evaluated under the following criteria. [0095] Good: At least seven
out of the ten golfers rated the ball as having a good feel [0096]
NG: Three or fewer of the ten golfers rated the ball as having a
good feel (A "good feel" refers to a feel having a suitably soft
touch; a feel which is too soft or too hard is a bad feel.)
[0097] In addition, the feel on shots with a putter was sensory
evaluated under the following criteria. [0098] Good: At least seven
out of the ten golfers rated the ball as having a good feel [0099]
NG: Three or fewer of the ten golfers rated the ball as having a
good feel
TABLE-US-00004 [0099] TABLE 4 Example Comparative Example 1 2 3 1 2
3 4 5 6 Core Diameter (mm) 38.8 38.8 38.8 38.8 35.9 38.8 38.8 37.2
38.8 Weight (g) 35.3 35.3 35.3 34.4 28.9 34.8 35.2 31.8 35.4
Deflection under 3.4 3.7 4.0 4.0 4.0 3.4 3.4 3.4 3.4 10-130 kgf
loading (mm) Surface hardness JIS-C 83 81 80 80 79 83 83 83 83
Shore D 55 54 52 52 52 55 55 55 55 Hardness 19.4 mm JIS-C 71 69 67
67 -- 71 71 -- 71 from center: A Shore D 46 44 43 43 -- 46 46 -- 46
(between core surface and center) Hardness 17.95 mm JIS-C -- -- --
-- 67 -- -- -- -- from center: A Shore D -- -- -- -- 43 -- -- -- --
(between core surface and center) Hardness 18.6 mm JIS-C -- -- --
-- -- -- -- 71 -- from center: A Shore D -- -- -- -- -- -- -- 46 --
(between core surface and center) Center hardness JIS-C 63 61 60 60
60 63 63 63 63 Shore D 40 39 38 38 38 40 40 40 40 Surface - Center
JIS-C 20 20 20 20 19 20 20 20 20 Shore D 15 15 14 14 14 15 15 15 15
(Surface + Center)/2: B (JIS-C) 73 71 70 70 70 73 73 73 73 B - A
(JIS-C) 2 2 3 3 3 2 2 2 2 Intermediate Material (type) No. 1 No. 1
No. 1 No. 1 No. 1 No. 5 No. 1 No. 1 No. 1 layer Specific gravity
1.07 1.07 1.07 1.07 1.07 1.19 1.07 1.07 1.07 Material hardness
(Shore D) 27 27 27 27 27 55 27 27 27 Melt index (at 190.degree. C.)
10 10 10 10 10 -- 10 10 10 Thickness (mm) 0.85 0.85 0.85 0.85 1.5
0.85 1.1 0.85 0.85 Intermediate Diameter (mm) 40.5 40.5 40.5 40.5
38.9 40.5 41 38.9 40.5 layer-covered Weight (g) 39.8 39.8 39.8 38.9
35.9 39.8 41.1 35.9 39.9 sphere Cover Material (type) No. 2 No. 2
No. 2 No. 3 No. 2 No. 4 No. 2 No. 2 No. 5 Specific gravity 0.98
0.98 0.98 1.14 0.98 0.98 0.98 0.98 0.96 Material hardness (Shore D)
63 63 63 63 63 45 63 63 53 Melt index (at 190.degree. C.) 3.2 3.2
3.2 -- 3.2 1 3.2 3.2 2.2 Thickness (mm) 1.1 1.1 1.1 1.1 1.9 1.1
0.85 1.9 1.1 Ball Diameter (mm) 42.7 42.7 42.7 42.7 42.7 42.7 42.7
42.7 42.7 Weight (g) 45.5 45.5 45.5 45.5 45.5 45.5 45.5 45.5 45.5
Cover thickness/Intermediate layer thickness 1.29 1.29 1.29 1.29
1.27 1.29 0.77 2.24 1.29 Core diameter/Cover thickness 35.3 35.3
35.3 35.3 18.9 35.3 45.6 19.6 35.3 Core diameter/Intermediate layer
thickness 45.6 45.6 45.6 45.6 23.9 45.6 35.3 43.8 45.6
TABLE-US-00005 TABLE 5 Example Comparative Example 1 2 3 1 2 3 4 5
6 Flight W#1 Total 179.7 179.5 179.3 176.5 177.7 173.5 177.8 177.6
174.0 (HS = distance 38 m/s) (m) Spin rate 3,030 2,948 2,866 3,103
3,236 3,210 3,100 3,125 3,234 (rpm) Distance good good good NG NG
NG NG NG NG (m) Feel on shots good good good good good good good
good good with W#1 Feel on shots good good good good good good good
good good with putter
[0100] As is apparent from Table 5, the respective Comparative
Examples were inferior to the Working Examples of the invention in
the following ways.
[0101] In Comparative Example 1, the cover material was composed
primarily of urethane, the spin rate was high and the rebound was
low, as a result of which a good distance was not achieved.
[0102] In Comparative Example 2, the combined thickness of the
cover and the intermediate layer was more than 2.2 mm and the spin
rate was high, as a result of which a good distance was not
achieved.
[0103] In Comparative Example 3, the cover was softer than the
intermediate layer, the Shore D hardness of the intermediate layer
material was higher than 50, and the spin rate was high, as a
result of which a good distance was not achieved.
[0104] In Comparative Example 4, the cover thickness/intermediate
layer thickness ratio was smaller than 1.1 and the spin rate was
high, as a result of which a good distance was not achieved.
[0105] In Comparative Example 5, the cover thickness/intermediate
layer thickness ratio was larger than 2.0 and the spin rate was
high, as a result of which a good distance was not achieved.
[0106] In Comparative Example 6, the Shore D hardness of the cover
material was softer than 60 and the spin rate was high, as a result
of which a good distance was not achieved.
* * * * *