U.S. patent application number 12/870493 was filed with the patent office on 2012-03-01 for multiple-piece golf ball.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. Invention is credited to Hiroshi HIGUCHI, Atsushi NANBA.
Application Number | 20120052981 12/870493 |
Document ID | / |
Family ID | 45697990 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120052981 |
Kind Code |
A1 |
NANBA; Atsushi ; et
al. |
March 1, 2012 |
MULTIPLE-PIECE GOLF BALL
Abstract
A multiple-piece golf ball in accordance with the present
invention includes a core located in the center of the golf ball,
at least two intermediate layers surrounding the core, and a cover
further surrounding the intermediate layers. The golf ball has a
spherical zone having a bulk specific gravity of about 0.7 or less,
the spherical zone having a radius of 18.5 mm with the same center
point as the golf ball. The moment of inertia of this golf ball is
preferably about 85 gcm.sup.2 or more.
Inventors: |
NANBA; Atsushi;
(Chichibu-shi, JP) ; HIGUCHI; Hiroshi;
(Chichibu-shi,, JP) |
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Family ID: |
45697990 |
Appl. No.: |
12/870493 |
Filed: |
August 27, 2010 |
Current U.S.
Class: |
473/371 |
Current CPC
Class: |
A63B 37/0056 20130101;
A63B 37/0064 20130101; A63B 37/0082 20130101; A63B 37/0076
20130101; A63B 37/0047 20130101 |
Class at
Publication: |
473/371 |
International
Class: |
A63B 37/02 20060101
A63B037/02 |
Claims
1. A multiple-piece golf ball comprising: a core located in a
center of the golf ball; at least two intermediate layers
surrounding the core; and a cover further surrounding the
intermediate layers, wherein the golf ball has a spherical zone
having a bulk specific gravity of up to about 0.7, the spherical
zone having a radius of 18.5 mm with the same center point as the
golf ball.
2. The golf ball according to claim 1, wherein the core includes a
hollow part in a center thereof and a surrounding layer surrounding
the hollow part.
3. The golf ball according to claim 2, wherein at least either one
of the innermost intermediate layer of the at least two
intermediate layers and the surrounding layer has a bulk specific
gravity of up to about 0.8.
4. The golf ball according to claim 2, wherein the hollow part has
a spherical shape having a diameter smaller than about 5 mm.
5. The golf ball according to claim 2, wherein the surrounding
layer is a foam.
6. The golf ball according to claim 2, wherein an intermediate
layer located in the spherical zone of the at least two
intermediate layers is a foam.
7. The golf ball according to claim 2, wherein the surrounding
layer has a space not filled with a material.
8. The golf ball according to claim 2, wherein an intermediate
layer located in the spherical zone of the at least two
intermediate layers has a space not filled with a material.
9. The golf ball according to claim 1, wherein the core is a
foam.
10. The golf ball according to claim 1, wherein the core has a
space not filled with a material.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a multiple-piece golf
ball.
[0002] There are many factors influencing the carry of a golf ball,
and among these factors, three factors of ball initial velocity,
delivery angle, and spin speed are regarded as very important.
Among these three factors, the ball spin is the essential factor
for raising the golf ball and increasing the carry. However, if the
spin speed is too high, the golf ball will be blown upward, or the
run of the ball after falling decreases, which prevents the carry
from increasing. The spin speed is the highest at the early stage
at which the golf ball is delivered, and decreases gradually, that
is, slows down during the flight of the golf ball.
[0003] Japanese Patent Application Publication No. 10-127815
discloses a golf ball having a moment of inertia of 81 to 86
gcm.sup.2, including a hollow core consisting of a hollow part
having a 5 to 25 mm diameter and a core outer layer part having a
specific gravity of about 1.2 to 1.9 surrounding the hollow part.
This Publication also discloses that the core of a two-piece solid
golf ball is made of two layers, and the specific gravity of the
inner layer hull is made small and that of the outer layer hull is
made large, whereby the moment of inertia of the golf ball is
increased.
[0004] Japanese Patent Application Publication No. 11-70189
discloses a golf ball including a hollow part having a diameter of
about 9 to 25 mm, a hollow core consisting of a material having a
specific gravity of 1.05 to 1.25, and a 1 to 3-mm thick resin layer
consisting of a material having an Izod impact strength of 50 J/m
or higher, formed on the inner surface of the hollow core. This
Publication also discloses that although the increase in the hollow
part increases the moment of inertia, the hollow core may be easily
broken by an impact force applied to the ball at the impact time;
however, the formation of the resin layer can prevent the hollow
core from being broken.
SUMMARY OF THE INVENTION
[0005] The above-described Publications disclose that the moment of
inertia of the golf ball is increased to increase the carry of the
golf ball, and also disclose that to increase the moment of
inertia, the core is caused to have a hollow part having the
largest possible diameter. However, if the diameter of the hollow
part is increased, there arises a problem of decreased durability
of the core and the golf ball. Also, if a material having a large
specific gravity, which provides a high strength, is used for a
core layer surrounding the hollow part to maintain the durability,
the specific gravity on the center side of golf ball becomes large,
so that the moment of inertia is decreased, which poses a problem
that the carry cannot be increased sufficiently.
[0006] Accordingly, an object of the present invention is to
provide a multiple-piece golf ball capable of increasing the moment
of inertia of the golf ball significantly and thereby increasing
the carry while the durability of the golf ball is maintained.
[0007] To achieve the above object, the present invention provides
a multiple-piece golf ball including a core located in the center
of the golf ball, at least two intermediate layers surrounding the
core; and a cover further surrounding the intermediate layers,
wherein the golf ball has a spherical zone having a bulk specific
gravity of up to about 0.7, the spherical zone having a radius of
18.5 mm with the same center point as the golf ball.
[0008] The core may include a hollow part in the center thereof and
a surrounding layer surrounding the hollow part. In this case,
preferably, at least either one of the innermost intermediate layer
of the at least two intermediate layers and the surrounding layer
has a bulk specific gravity of about 0.8 or less. The innermost
intermediate layer of the at least two intermediate layers is
usually in the spherical zone. The hollow part preferably has a
spherical shape having a diameter less than about 5 mm. The
surrounding layer may be a foam or may have a space not filled with
a material. Also, an intermediate layer located in the spherical
zone of the at least two intermediate layers may be a foam or may
have a space not filled with a material.
[0009] The core may be a foam in place of the above-described
hollow core. Also, an intermediate layer located in the spherical
zone of the at least two intermediate layers may be a foam.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a sectional view showing one embodiment of a
multiple-piece golf ball in accordance with the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] An embodiment of a multiple-piece golf ball in accordance
with the present invention will now be described with reference to
the accompanying drawing. The present invention is not limited to
this embodiment. The accompanying drawing is not drawn scaled down
for better understanding of the present invention.
[0012] As shown in FIG. 1, a multiple-piece golf ball of this
embodiment mainly includes a core 10 located in the central portion
of the ball, intermediate layers 20 surrounding the outside of the
core 10, and a cover 30 surrounding the outside of the intermediate
layers 20. The design is made so that the bulk specific gravity of
a spherical zone having a radius R of 18.5 mm with the center point
C of the golf ball 1 being the center is very small, being about
0.7 or smaller. In this specification, the "bulk specific gravity"
is represented by the ratio of the mass of a predetermined zone to
the mass of 4.degree. C. pure water. The whole interior of the zone
need not be filled with a material, and a space such as a cavity or
air bubbles may be present in the zone.
[0013] By this configuration, the center side of the golf ball 1 is
made light and the outside thereof is made heavy, so that the
moment of inertia of the golf ball 1 can be increased. Therefore,
since the spin decay rate during flight decreases, even when the
initial spin speed is low, the spin speed during flight is
maintained in a proper range, so that the carry can be increased.
The upper limit of bulk specific gravity of the above-described
zone is preferably about 0.75, further preferably about 0.725. The
lower limit of bulk specific gravity of the above-described zone is
not subject to any special restriction, but is preferably about
0.2, more preferably about 0.3.
[0014] The moment of inertia of the golf ball 1 should be designed
so as to be preferably about 85 gcm.sup.2 or higher, more
preferably about 90 gcm.sup.2 or higher, and still more preferably
about 95 gcm.sup.2 or higher. The upper limit of the moment of
inertia of the golf ball 1 is not subject to any special
restriction, but is preferably about 120 gcm.sup.2, more preferably
about 118 gcm.sup.2, and still more preferably about 115 gcm.sup.2.
Also, the spin decay rate should be designed so as to be preferably
about 2.65% or lower, more preferably about 2.6% or lower. The
lower limit of the spin decay rate is not subject to any special
restriction, but is preferably about 2.0%, more preferably about
2.2%.
[0015] Hereunder, the constructions of the core 10, the
intermediate layers 20, and the cover 30 of the golf ball 1 having
the above-described configuration are explained in detail.
[0016] The core 10 includes a hollow part 10a located in the
central portion of the core 10 and a surrounding layer 10b
surrounding the outside of the hollow part 10a. The hollow part 10a
substantially has a spherical shape. The surrounding layer 10b
substantially has a spherical external shape.
[0017] The lower limit of the diameter of the hollow part 10a is
preferably about 2 mm, more preferably about 3 mm. On the other
hand, the upper limit of the diameter of the hollow part 10a is
preferably about 5 mm, more preferably about 4 mm. The lower limit
of the outside diameter of the core 10 is preferably about 6 mm,
more preferably about 7 mm. The upper limit of the outside diameter
of the core 10 is preferably about 35 mm, more preferably about 34
mm. The lower limit of the thickness of the surrounding layer 10b
is preferably about 2 mm, more preferably about 2.5 mm. The upper
limit of the thickness of the surrounding layer 10b is preferably
about 18 mm, more preferably about 17 mm.
[0018] The lower limit of the bulk specific gravity of the
surrounding layer 10b is preferably about 0.2, more preferably
about 0.3, and still more preferably about 0.4. The upper limit of
the bulk specific gravity of the surrounding layer 10b is
preferably about 4.0, more preferably about 3.8, and still more
preferably about 3.6. It is preferable that the bulk specific
gravity of either one of the surrounding layer 10b and the
later-described first intermediate layer 20a be made 0.8 or
smaller.
[0019] As a material forming the core 10 or the surrounding layer
10b, for example, a rubber composition containing a base rubber,
being a principal component, and optionally containing a
co-crosslinking agent, an initiator, a filler, a foaming agent, an
antioxidant, and an organo-sulfur compound can be used. Also, as
the principal component, in place of the base rubber, a
thermoplastic elastomer, an ionomer resin, or a mixture thereof can
be used.
[0020] As the base rubber, a thermosetting elastomer can be used
widely, and, for example, 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 can be used. However, the
base rubber is not limited to these rubbers. As the polybutadiene
rubber (BR), for example, 1,2-polybutadiene, c is
1,4-polybutadiene, and the like can be used.
[0021] Polybutadiene preferably has a Mooney viscosity (ML.sub.1+4
(100.degree. C.)) of about 30 or higher. The Mooney viscosity
thereof is more preferably about 35 or higher, still more
preferably about 40 or higher, yet still more preferably about 50
or higher, and most preferably about 52 or higher. The upper limit
of the Mooney viscosity thereof is preferably about 100, more
preferably about 80, still more preferably about 70, and yet still
more preferably about 60.
[0022] The Mooney viscosity in the present invention is an
industrial viscosity index (JIS-K6300) measured by a Mooney
viscometer, which is one kind of rotary plasticity meter, and as
the unit symbol thereof, ML.sub.1+4 (100.degree. C.) is used. In
this unit symbol, M denotes Mooney viscosity, L denotes a large
rotor (L type), 1+4 denotes that the preheating time is one minute
and the rotor rotating time is four minutes, and 100.degree. C.
denotes that measurement is made under a condition of 100.degree.
C.
[0023] Furthermore, the molecular weight distribution Mw/Mn (Mw:
weight-average molecular weight, Mn: number-average molecular
weight) of polybutadiene is preferably about 2.0 or more, more
preferably about 2.2 or more, still more preferably about 2.4 or
more, and yet still more preferably about 2.6 or more. The upper
limit of the molecular weight distribution thereof is preferably
about 6.0, more preferably about 5.0, still more preferably about
4.0, and yet still more preferably about 3.4. If Mw/Mn is too low,
the workability may deteriorate, and if Mw/Mn is high, the
resilience performance may degrade.
[0024] Although polybutadiene may be synthesized by using a Ni or
Co catalyst, or may be synthesized by using a rare earth element
based catalyst; in particular, polybutadiene is preferably
synthesized by using a rare earth element based catalyst. As the
rare earth element based catalyst, a publicly known rare earth
element based catalyst can be used. For example, a lanthanoid rare
earth element based compound, an organic aluminum compound,
alumoxane, and a halogen-containing compound, and further, a
catalyst consisting of a combination of Lewis base as necessary can
be cited.
[0025] In the present invention, in particular, the use of a
neodymium based catalyst using a neodymium compound as the
lanthanoid rare earth element compound is preferable because
polybutadiene rubber having a high content of 1,4-cis bond and a
low content of 1,2-vinyl bond is obtained with excellent
polymerization activity. As the specific examples of the rare earth
element based catalyst, the catalysts described in Japanese
Unexamined Patent Application Publication No. 11-35633 can be cited
preferably, the citation thereof herein forming a part of
description of this specification.
[0026] In the case in which butadiene is polymerized in the
presence of the rare earth element based catalyst, a solvent may be
used, or bulk polymerization or vapor-phase polymerization may be
made without the use of solvent. The polymerization temperature can
be made usually about -30.degree. C. to about 150.degree. C.,
preferably about 10 to 100.degree. C.
[0027] The above-described polybutadiene may be obtained by
allowing a terminal modifying agent to react with the active
terminal of polymer following the polymerization using the rare
earth element based catalyst. As the specific examples and the
reaction methods of the terminal modifying agent, for example, the
terminal modifying agents and the reaction methods described in
Japanese Unexamined Patent Application Publication Nos. 11-35633,
07-268132, and 2002-293996 can be cited, the citation thereof
herein forming a part of description of this specification.
[0028] Polybutadiene is blended in the rubber base material
preferably in an amount of about 60 wt % or more, more preferably
in the amount of about 70 wt % or more, still more preferably in
the amount of about 80 wt % or more, and most preferably in the
amount of about 90 wt % or more. The upper limit of the blend ratio
of polybutadiene is preferably about 100 wt %. By blending
polybutadiene within this range, a golf ball having satisfactory
resilience performance can be obtained.
[0029] Also, the aforementioned rubber other than polybutadiene can
be blended, in addition to polybutadiene, in a range so as not to
compromise the object of the present invention. The rubbers
especially preferable for being blended in addition to
polybutadiene are styrene-butadiene rubber, natural rubber,
polyisoprene rubber, ethylene-propylene-diene rubber, and the like.
These rubbers can be used singly in one kind, or can be used by
combining two or more kinds.
[0030] As the co-crosslinking agent, although not limited thereto,
for example, .alpha.,.beta.-unsaturated carboxylic acid or a
metallic salt thereof can preferably be used. As the
.alpha.,.beta.-unsaturated carboxylic acid or the metallic salt
thereof, for example, acrylic acid, methacrylic acid, and a zinc
salt, magnesium salt, calcium salt, and the like thereof can be
cited. As the blending amount of the co-crosslinking agent,
although not limited to this, for example, with respect to 100
weight parts of rubber base material, about 5 weight parts or more
is preferable, and about 10 weight parts or more is more
preferable. Also, the blending amount of the co-crosslinking agent
is preferably about 70 weight parts or less, more preferably about
50 weight parts or less.
[0031] As the initiator, although not limited to this, an organic
peroxide is preferably used. As the blending amount of the
initiator, although not limited to this, for example, with respect
to 100 weight parts of rubber base material, about 0.10 weight part
or more is preferable, about 0.15 weight part or more is more
preferable, and about 0.30 weight part or more is still more
preferable. Also, the blending amount of the initiator is
preferably about 8 weight parts or less, more preferably about 6
weight parts or less.
[0032] As the filler, for example, silver, gold, cobalt, chromium,
copper, iron, germanium, manganese, molybdenum, nickel, lead,
platinum, tin, titanium, tungsten, zinc, zirconium, barium sulfate,
zinc oxide, manganese oxide, and the like can be used, but the
filler is not limited to these. The filler is preferably in a
powder form. As the blending amount of the filler, although not
limited to this, for example, with respect to 100 weight parts of
rubber base material, about 2 weight parts or more is preferable,
about 5 weight parts or more is more preferable, and about 10
weight parts or more is still more preferable. Also, the blending
amount of the filler is preferably about 1000 weight parts or less,
more preferably about 900 weight parts or less, and still more
preferably about 800 weight parts or less.
[0033] As the foaming agent, although not limited to this, for
example, azodicarbonamide, azobisisobutyronitrile,
dinitrosopentamethylenetetramine, p-toluenesulfonylhydrazide,
p,p'-oxybis (benzenesulfonylhydrazide), and sodium
hydrogencarbonate, can be used. As the blending amount of the
foaming agent, although not limited to this, for example, with
respect to 100 weight parts of rubber base material, about 2 weight
parts or more is preferable, and about 3 weight parts or more is
more preferable. Also, the blending amount of the foaming agent is
preferably about 30 weight parts or less, more preferably about 25
weight parts or less.
[0034] Although FIG. 1 shows the core 10 the central portion of
which is hollow, the present invention is not limited to this
configuration, and a solid core may be used. Also, the core 10 or
the surrounding layer 10a may be formed so as to have a space that
is not filled with a material. Such a space, for example, may be a
concave-shaped space formed by depressing a part of a layer
surface, or may be a hole-shaped space penetrating the layer.
Alternatively, a space can be provided in the core 10 or the
surrounding layer 10a by adding a foaming agent to the material of
the core 10 or the surrounding layer 10a. As the foaming agent, the
above-described foaming agent can be used. As the blending amount
of the foaming agent, although not limited to this, for example,
with respect to 100 weight parts of principal component, about 2
weight parts or more is preferable, and about 3 weight parts or
more is more preferable. Also, the blending amount of the foaming
agent is preferably about 30 weight parts or less, more preferably
about 25 weight parts or less.
[0035] The intermediate layers 20 include the first intermediate
layer 20a on the center side and a second intermediate layer 20b on
the outside. The distance from the center C of the golf ball 1 to
the outside surface of the first intermediate layer 20a is a
distance D of 18.5 mm as described above. The lower limit of the
thickness of the first intermediate layer 20a is preferably about
0.5 mm, more preferably about 1.0 mm, and still more preferably
about 1.5 mm. The upper limit of the thickness of the first
intermediate layer 20a is preferably about 16 mm, more preferably
about 15 mm, and still more preferably about 14 mm.
[0036] The bulk specific gravity of the first intermediate layer
20a is preferably about 0.2 or larger, more preferably about 0.3 or
larger, and still more preferably about 0.4 or larger. The upper
limit of the bulk specific gravity of the first intermediate layer
20a is preferably about 3.8, more preferably about 3.6. It is
preferable that the bulk specific gravity or either one of the
surrounding layer 10b and the first intermediate layer 20a be made
0.8 or smaller.
[0037] The lower limit of the thickness of the second intermediate
layer 20b is preferably about 0.5 mm, more preferably about 0.8 mm,
and still more preferably about 1.0 mm. The upper limit of the
thickness of the second intermediate layer 20b is preferably about
16 mm, more preferably about 15 mm, and still more preferably about
14 mm.
[0038] The bulk specific gravity of the second intermediate layer
20b is preferably about 0.2 or greater, more preferably about 0.3
or greater, and still more preferably about 0.4 or greater. The
upper limit of the bulk specific gravity of the second intermediate
layer 20b is preferably about 3.8, and more preferably about
3.6.
[0039] As the material for the first and second intermediate layers
20a and 20b, although not limited to this, a thermosetting
elastomer, a thermoplastic elastomer, an ionomer resin, or a
mixture thereof can be used.
[0040] As the thermosetting elastomer, although not limited to
this, 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 can be used.
[0041] Polybutadiene preferably has a Mooney viscosity (ML.sub.1+4
(100.degree. C.)) of about 30 or higher. The Mooney viscosity
thereof is more preferably about 35 or higher, still more
preferably about 40 or higher, yet still more preferably about 50
or higher, and most preferably about 52 or higher. The upper limit
of the Mooney viscosity thereof is preferably about 100, more
preferably about 80, still more preferably about 70, and yet still
more preferably about 60.
[0042] The Mooney viscosity in the present invention is an
industrial viscosity index (JIS-K6300) measured by a Mooney
viscometer, which is one kind of rotary plasticity meters, and as
the unit symbol thereof, ML.sub.1+4 (100.degree. C.) is used. In
this unit symbol, M denotes Mooney viscosity, L denotes a large
rotor (L type), 1+4 denotes that the preheating time is one minute
and the rotor rotating time is four minutes, and 100.degree. C.
denotes that measurement is made under conditions of 100.degree.
C.
[0043] Furthermore, the molecular weight distribution Mw/Mn (Mw:
weight-average molecular weight, Mn: number-average molecular
weight) of polybutadiene is preferably about 2.0 or more, more
preferably about 2.2 or more, still more preferably about 2.4 or
more, and yet still more preferably about 2.6 or more. The upper
limit of the molecular weight distribution thereof is preferably
about 6.0, more preferably about 5.0, still more preferably about
4.0, and yet still more preferably about 3.4. If Mw/Mn is too low,
the workability may deteriorate, and if Mw/Mn is too high, the
resilience performance may degrade.
[0044] Although polybutadiene may be synthesized by using a Ni or
Co catalyst, or may be synthesized by using a rare earth element
based catalyst, in particular, polybutadiene is preferably
synthesized by using a rare earth element based catalyst. As the
rare earth element based catalyst, a publicly known rare earth
element based catalyst can be used. For example, a lanthanoid rare
earth element compound, an organic aluminum compound, alumoxane,
and a halogen-containing compound, and furthermore a catalyst
consisting of a combination of Lewis base as necessary can be
cited.
[0045] In the present invention, in particular, the use of a
neodymium based catalyst using a neodymium compound as the
lanthanoid rare earth element compound is preferable because
polybutadiene rubber having a high content of 1,4-cis bond and a
low content of 1,2-vinyl bond is obtained with excellent
polymerization activity. As the specific examples of the rare earth
element based catalyst, the catalysts described in Japanese
Unexamined Patent Application Publication No. 11-35633 can be cited
preferably, the citation thereof herein forming a part of
description of this specification.
[0046] In the case in which butadiene is polymerized in the
presence of the rare earth element based catalyst, a solvent may be
used, or bulk polymerization or vapor-phase polymerization may be
made without the use of solvent. The polymerization temperature can
be made usually about -30.degree. C. to about 150.degree. C.,
preferably about 10 to 100.degree. C.
[0047] The above-described polybutadiene may be obtained by
allowing a terminal modifying agent to react with the active
terminal of polymer following the polymerization using the rare
earth element based catalyst. As the specific examples and the
reaction methods of the terminal modifying agent, for example, the
terminal modifying agents and the reaction methods described in
Japanese Unexamined Patent Applications Publications Nos. 11-35633,
07-268132, and 2002-293996 can be cited, the citation thereof
herein forming a part of description of this specification.
[0048] Polybutadiene is blended in the rubber base material
preferably in the amount of about 60 wt % or more, more preferably
in the amount of about 70 wt % or more, still more preferably in
the amount of about 80 wt % or more, and most preferably in the
amount of about 90 wt % or more. The upper limit of the blend ratio
of polybutadiene is preferably about 100 wt %. By blending
polybutadiene within this range, a golf ball having satisfactory
resilience performance can be obtained.
[0049] Also, the aforementioned rubber other than polybutadiene can
be blended, in addition to polybutadiene, in a range that does not
compromise the object of the present invention. The rubbers
especially preferable for being blended in addition to
polybutadiene are styrene-butadiene rubber, natural rubber,
polyisoprene rubber, ethylene-propylene-diene rubber, and the like.
These rubbers can be used alone as one kind, or can be used by
combining two or more kinds.
[0050] As the thermoplastic elastomer, although not limited to
this, for example, a polyester based thermoplastic elastomer, a
polyurethane based thermoplastic elastomer, a polyamide based
thermoplastic elastomer, and a polyolefin based thermoplastic
elastomer can be used.
[0051] As the ionomer resin, although not limited to this, a resin
using the following (a) component and/or (b) component as a base
resin can be used. To the base resin, the following (c) component
can be added optionally. The (a) component is a tertiary random
copolymer of olefin-unsaturated carboxylic acid-unsaturated
tertiary random copolymer of olefin-unsaturated carboxylic
acid-unsaturated carboxylate carboxylate and/or a metallic salt
thereof, the (b) component is a binary random copolymer of
olefin-unsaturated carboxylic acid and/or a metallic salt thereof,
and the (c) component is a thermoplastic block copolymer having a
polyolefin crystal block polyethylene/butylene random
copolymer.
[0052] The weight-average molecular weight (Mw) of the tertiary
random copolymer of olefin-unsaturated carboxylic acid-unsaturated
carboxylate and/or the metallic salt thereof constituting the (a)
component is preferably about 100,000 or greater, more preferably
about 110,000 or greater, and still more preferably about 120,000
or greater. The upper limit thereof is preferably about 200,000,
more preferably about 190,000, and still more preferably about
170,000. Also, the ratio of the weight-average molecular weight
(Mw) to the number-average molecular weight (Mn) of the copolymer
is preferably about 3.0 to about 7.0.
[0053] The (a) component is a copolymer containing olefin, and as
the olefin in the (a) component, for example, an olefin having a
carbon number of 2 or more, the upper limit of which is 8 or less,
especially 6 or less, can be mentioned. Specifically, ethylene,
propylene, butene, pentene, hexene, heptene, and octene can be
mentioned, and in particular, ethylene is preferable.
[0054] As the unsaturated carboxylic acid in the (a) component, for
example, acrylic acid, methacrylic acid, maleic acid, and fumaric
acid can be cited, and in particular, acrylic acid and methacrylic
acid are preferable.
[0055] As the acid-unsaturated carboxylate in the (a) component,
for example, a lower alkylester of the above-described carboxylic
acid can be cited. Specifically, methyl methacrylate, ethyl
methacrylate, propyl methacrylate, butyl methacrylate, methyl
acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate can
be cited, and in particular, butyl acrylate (n-butyl acrylate,
i-butyl acrylate) is preferable.
[0056] The random copolymer of the (a) component can be obtained by
random copolymerizing the above-described components according to
the publicly known method. Herein, the content (acid content) of
unsaturated carboxylic acid contained in the random copolymer is
usually about 2 wt % or higher, preferably about 6 wt % or higher,
and more preferably about 8 wt % or higher. The upper limit thereof
is about 25 wt %, preferably about 20 wt %, and more preferably
about 15 wt %. If the acid content is low, the resilience
performance may degrade, and if the acid content is high, the
workability of the material may deteriorate.
[0057] The metallic salt of the copolymer of the (a) component can
be obtained by partially neutralizing the acid radical in the
random copolymer of the above-described (a) component with metal
ion.
[0058] Herein, as the metal ion for neutralizing the acid radical,
for example, ions of Na, K, Li, Zn, Cu, Mg, Ca, Co, Ni and Pb can
be cited, and among these, ions of Na, Li, Zn, Mg and Ca are
preferably used, and more preferably, Zn ion is recommended. The
degree of neutralization of random copolymer of these ions is not
subject to any special restriction; however, being usually about 5
mol % or more, preferably about 10 mol % or more, and especially
about 20 mol % or more. The upper limit thereof is usually about 95
mol %, preferably about 90 mol %, and especially about 80 mol %. If
the degree of neutralization exceeds about 95 mol %, the
formability may deteriorate. If it is lower than about 5 mol %, the
addition amount of the inorganic metallic compound of an (e)
component must be increased, which may be disadvantageous in terms
of cost. Such a neutralizer can be obtained by a publicly known
method, and, for example, can be obtained by introducing a compound
of formate, acetate, nitrate, carbonate, hydrogencarbonate, oxide,
hydroxide, and alkoxide of the metal ion to the random
copolymer.
[0059] As the tertiary random copolymer of olefin-unsaturated
carboxylic acid-unsaturated carboxylate constituting the (a)
component, specifically, trade names "Nucrel AN4318", "Nucrel
AN4319", "Nucrel AN4311" (manufactured by DuPont-Mitsui
Polychemicals Co., Ltd.) and the like can be cited. Also, as the
metallic salt of tertiary random copolymer of olefin-unsaturated
carboxylic acid-unsaturated carboxylate, specifically, trade names
"Himilan AM7316", "Himilan AM7331", "Himilan 1855", "Himilan 1856"
(manufactured by DuPont-Mitsui Polychemicals Co., Ltd.), trade
names "Surlyn 6320", "Surlyn 8120" (manufactured by DuPont U.S.A),
and the like can be cited.
[0060] Also, the weight-average molecular weight (Mw) of the binary
random copolymer of olefin-unsaturated carboxylic acid and/or a
metallic salt thereof constituting the (b) component is preferably
about 100,000 or greater, more preferably about 110,000 or greater,
and still more preferably about 120,000 or greater. The upper limit
thereof is preferably about 200,000, more preferably about 190,000,
and still more preferably about 170,000. Also, the ratio of the
weight-average molecular weight (Mw) to the number-average
molecular weight (Mn) of the copolymer is preferably about 3.0 to
about 7.0.
[0061] The ratio of the copolymer of the (b) component to the whole
of the base resin is about 0 to about 20 wt %, and the lower limit
thereof is preferably 1 wt %. The upper limit value thereof is
preferably about 17 wt %, more preferably about 10 wt %, still more
preferably about 8 wt %, and yet still more preferably about 5 wt
%.
[0062] As a special example of the binary random copolymer of
olefin-unsaturated carboxylic acid constituting the (b) component,
trade names "Nucrel 1560", "Nucrel 1525", "Nucrel 1035", and the
like (manufactured by DuPont-Mitsui Polychemicals Co., Ltd.) can be
cited. As the metallic salt of binary random copolymer of
olefin-unsaturated carboxylic acid, specifically, trade names
"Himilan 1605", "Himilan 1601", "Himilan 1557", "Himilan 1705",
"Himilan 1706" (manufactured by DuPont-Mitsui Polychemicals Co.,
Ltd.), trade names "Surlyn 7930", "Surlyn 7920" (manufactured by
DuPont U.S.A), and the like can be cited.
[0063] As the thermoplastic, block copolymer having a polyolefin
crystal block polyethylene/butylene random copolymer constituting
the (c) component, for example, a copolymer having a crystalline
polyethylene block (E) as a hard segment and a block consisting of
a relatively random copolymer (EB) of ethylene and butylene as a
soft segment can be cited, and a block copolymer having a structure
of an E-EB system, E-EB-E system, and the like in which the hard
segment lies at one terminal or both terminals as a molecular
structure is preferably used.
[0064] The thermoplastic block copolymer having a polyolefin
crystal block polyethylene/butylene random copolymer constituting
the (c) component can be obtained, for example, by hydrogenating
polybutadiene. As the polybutadiene used for hydrogenation,
polybutadiene, in which as the bond mode in the butadiene
structure, especially a 1,4-bond has a 1,4-polymerization part of
about 95 to about 100 wt % in terms of a block, and the 1,4-bond in
the total amount of butadiene structure is preferably about 50 to
about 100 wt %, more preferably about 80 to about 100 wt %, is
suitably used. That is, polybutadiene in which the 1,4-bond is
preferably about 50 to about 100 wt %, more preferably about 80 to
about 100 wt %, and which has a 1,4-bond part of about 95 to about
100 wt % in terms of a block is suitably used.
[0065] As the thermoplastic block copolymer of an E-EB-E system, a
copolymer, in which both terminal parts of a molecular chain are
1,4-bond rich 1,4-polymerized substances, and the intermediate part
is obtained by hydrogenating polybutadiene in which 1,4-bond and
1,2-bond are mixed, is suitable. Herein, the hydrogenation amount
in hydrogenated substance of polybutadiene (the conversion ratio of
the double bond in polybutadiene to the saturation bond) is
preferably about 60 to about 100%, more preferably about 90 to
about 100%. If the hydrogenation amount is too small, in a process
of blending with ionomer resin or the like, gelation and the like
may be deteriorated. Also, when the golf ball is formed, the
intermediate layers may pose a problem of poor hitting
durability.
[0066] In the block copolymer that is used suitably as the
thermoplastic block copolymer, and has a structure of an E-EB
system, E-EB-E system, in which the hard segment lies at one
terminal or both terminals as a molecular structure, the amount of
hard segment is preferably about 10 to about 50 wt %. If the amount
of hard segment is too large, the object of the present invention
is not achieved effectively in some cases, and if the amount of
hard segment is too small, there arises a problem of poor
formability of blended substance in some cases.
[0067] The melt index at a temperature of 230.degree. C. and a test
load of 21.2 N of the thermoplastic block copolymer is preferably
about 0.01 to about 15 g/10 min, more preferably about 0.03 to
about 10 g/10 min. If the melt index is out of the above-described
range, a problem of welding, sinking, being short, and the like may
occur. Also, the surface hardness of thermoplastic block copolymer
is preferably 10 to 50. If the surface hardness is too low, the
durability in repeated hitting of the golf ball may deteriorate. On
the other hand, if the surface hardness is too high, the resilience
performance of blended substance with ionomer resin may degrade.
The number-average molecular weight of the thermoplastic block
copolymer is preferably about 30,000 to about 800,000.
[0068] As the above-described thermoplastic block copolymer having
a polyolefin crystal block polyethylene/butylene random copolymer,
a commercially available product can be used, and as the copolymer,
for example, Dynaron 6100P, 6200P, 6201B, and the like manufactured
by Japan Synthetic Rubber Co., Ltd., can be cited. In particular,
Dynaron 6100P is a block polymer having a crystalline olefin block
at both terminals, and can be used suitably in the present
invention. These olefin-based thermoplastic elastomers may be used
singly in one kind, or can be used by combining two or more
kinds.
[0069] Furthermore, for the material of the intermediate layers 20,
with respect to 100 weight parts of the above-described resin
components of (a) to (c) components, about 5 to about 100 weight
parts of fatty acid having a molecular weight of about 280 to about
1500 or the derivative thereof can be mixed as a (d) component, and
about 0.1 to about 10 weight parts of a basic inorganic metallic
compound capable of neutralizing the acid radical in the (a), (b)
and (d) components can be mixed as the (e) component.
[0070] The (d) component is a fatty acid having a molecular weight
of about 280 to about 1500 or a derivative thereof, and is a
component contributing to the improvement in the flowability of the
heated mixture. Comparing with the (a) to (c) components, the (d)
component has an extremely low molecular weight, so that it
contributes to a remarkable increase in the melt viscosity of the
mixture. Also, the fatty acid (or derivative) in the (d) component
has a molecular weight not lower than about 280 and not higher than
about 1500 and contains a high-content acid radical (or
derivative), so that a loss of resilience performance due to
addition is small.
[0071] The fatty acid or the derivative thereof of the (d)
component may be an unsaturated fatty acid (derivative) containing
a double bond or a triple bond in an alkyl group, or may be
saturated fatty acid (derivative) in which the bond in the alkyl
group is formed by a single bond only. The number of carbons in one
molecule is usually about 18 or greater, and it is recommended that
the upper limit of the number of carbons be about 80, especially
about 40. If the number of carbons is small, the heat resistance
deteriorates, and the content of acid radical becomes too high, so
that desired flowability cannot be attained because of the
interaction with the acid radical contained in the base resin. If
the number of carbons is large, the flowability may decrease
because of the increase in molecular weight, so that the (d)
component may become difficult to use as a material.
[0072] As the fatty acid of the (d) component, specifically,
stearic acid, 12-hydroxystearic acid, behenic acid, oleic acid,
linolic acid, linolenic acid, arachidic acid, lignoceric acid, and
the like can be cited, and in particular, stearic acid, arachidic
acid, behenic acid, and lignoceric acid can be used suitably.
[0073] Also, as the fatty acid derivative of the (d) component, a
derivative in which a proton contained in the acid radical of fatty
acid is substituted can be cited. As such a fatty acid derivative,
a metallic soap substituted by metal ion can be cited as an
example. As the metal ion used for the metallic soap, ions of, for
example, Li, Ca, Mg, Zn, Mn, Al, Ni, Fe, Cu, Sn, Pb and Co can be
cited, and in particular, ions of Ca, Mg and Zn are preferable. The
Fe ion may be bivalent or trivalent.
[0074] As the fatty acid derivative of the (d) component,
specifically, 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, zinc lignocerate, and
the like can be cited, and in particular, 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 can be used suitably.
[0075] As the blending amount of the (d) component, usually, with
respect to 100 weight parts of the base resin, about 1 weight part
or more is preferable. The upper limit of the blending amount
thereof is usually about 100 weight parts, preferably about 90
weight parts, more preferably about 80 weight parts, and still more
preferably about 70 weight parts.
[0076] When the above-described (a) and/or (b) component is used,
publicly known metallic soap-denatured ionomer (U.S. Pat. No.
5,312,857, U.S. Pat. No. 5,306,760, WO 98/46671, and the like, the
citation thereof herein forming a part of the description of this
specification) can also be used.
[0077] The (e) component is a basic inorganic metallic compound
capable of neutralizing the acid radical in the (a), (b) and (d)
components. As described in the conventional example, when only the
(a), (b) or (d) component, especially only metallic soap-denatured
ionomer resin (for example, only the metallic soap-denatured
ionomer resin described in the aforementioned Patent Publications)
is heatedly mixed, fatty acid is yielded by exchange reaction of
metallic soap with unneutralized acid radical contained in ionomer
as shown below. This yielded fatty acid has low thermal stability,
and vaporizes easily at the time of formation. Therefore, this
fatty acid not only may cause poor formation but also may cause a
remarkable decrease in paint film adhesion when the yielded fatty
acid adheres to the surface of a formed product. The (e) component
is blended to solve such a problem.
##STR00001##
(1) Unneutralized acid radical contained in ionomer resin (2)
Metallic soap (3) Fatty acid X: Metal cation
[0078] For the heated mixture used in the present invention, as
described above, as the (e) component, the basic inorganic metallic
compound capable of neutralizing the acid radical contained in the
(a), (b) and (d) components is blended as an essential component.
By blending the (e) component, the acid radical in the (a), (b) and
(d) components is neutralized. Therefore, by the synergistic effect
due to the blending of these components, the thermal stability of
the heated mixture is increased, and at the same time, excellent
formability is provided, which contributes to enhanced resilience
performance as a golf ball.
[0079] The (e) component is a basic inorganic metallic compound
capable of neutralizing the acid radical in the (a), (b) and (d)
components, and it is recommended that the (e) component be
preferably a monoxide or a hydroxide. Since having great reactivity
with ionomer resin and containing no organic substance in the
reaction byproduct, the (e) component can increase the degree of
neutralization of heated mixture without impairing the thermal
stability.
[0080] As the metal ion used for the basic inorganic metallic
compound, for example, ions of Li, Na, K, Ca, Mg, Zn, Al, Ni, Fe,
Cu, Mn, Sn, Pb, Co and the like can be cited. As the inorganic
metallic compound, a basic inorganic filler containing these metal
ions, specifically, magnesium oxide, magnesium hydroxide, magnesium
carbonate, zinc oxide, sodium hydroxide, sodium carbonate, calcium
oxide, calcium hydroxide, lithium hydroxide, lithium carbonate, and
the like can be cited. As described above, a monoxide or a
hydroxide is suitable, and preferably, magnesium oxide or calcium
hydroxide that has great reactivity with ionomer resin can be used
suitably.
[0081] The blending amount of the (e) component is usually about
0.1 to about 10 weight parts with respect to 100 weight parts of
the base resin. The lower limit of the blending amount thereof is
preferably about 0.5 weight part, more preferably about 1 weight
part. The upper limit thereof is preferably about 5 weight parts,
more preferably about 3 weight parts.
[0082] The heated mixture used in the present invention is obtained
by blending the (a) to (e) components as described above, and is
used to improve the thermal stability, formability, and resilience
performance. For the heated mixture used in the present invention,
it is recommended that about 70 mol % or more, preferably about 80
mol % or more, and more preferably about 90 mol % or more of acid
radical in the mixture be neutralized. This high neutralization
more reliably restrains the exchange reaction that presents a
problem when only the above-described (a) and (b) components and
fatty acid (derivative) are used, and can prevent fatty acid from
being yielded. Therefore, there can be provided a material having
remarkably increased thermal stability, excellent formability, and
resilience performance remarkably upgraded as compared with the
conventional ionomer resin.
[0083] Regarding the neutralization of the heated mixture of the
present invention, to more reliably attain both the high degree of
neutralization and the flowability, it is recommended that the acid
radical of the heated mixture be neutralized by transition metal
ion and alkali metal and/or alkaline-earth metal ion. Since the
transition metal ion has a weaker ionic cohesive force than the
alkali metal and/or alkaline-earth metal ion, some of acid radical
in the heated mixture is neutralized, so that the flowability can
be improved remarkably.
[0084] In the present invention, to the heated mixture, various
addition agents can be further added as necessary; for example, a
filler, pigment, dispersing agent, antioxidant, ultraviolet light
absorbing agent, and light stabilizer can be added. Also, to
improve the feeling at the hitting time, in addition to the
above-described essential components, various nonionomer
thermoplastic elastomers can be blended. As the nonionomer
thermoplastic elastomer, for example, styrene based thermoplastic
elastomer, ester based thermoplastic elastomer, and urethane based
thermoplastic elastomer can be cited, and in particular, styrene
based thermoplastic elastomer is used preferably.
[0085] As a method for preparing the heated mixture, for example,
an internal mixer such as a twin-screw extruder, a Banbury mixer,
and a kneader is used, and as the condition of mixing by heating,
for example, mixing is performed while heating to about 150 to
about 250.degree. C. is performed. The method for forming the
intermediate layers by using the above-described heated mixture is
not subject to any special restriction, and the intermediate layers
can be formed, for example, by injection molding or compression
molding. In the case in which the injection molding method is used,
a method can be used in which after a solid core prepared in
advance has been placed at a predetermined position in a mold for
injection molding, the above-described material is introduced into
the mold. Also, in the case in which the compression molding method
is used, a method can be used in which a pair of half cups are
prepared using the above-described material, the core is wrapped
with these cups directly or via the intermediate layers, and
pressure and temperature are applied in the mold. In the case in
which molding is performed under pressure and temperature, as the
molding conditions, the conditions of about 120 to about
170.degree. C. and about 1 minute to about 5 minutes can be
adopted.
[0086] To the first and second intermediate layers 20a and 20b, a
filler or a foaming agent can be added optionally in addition to
the above-described principal components of rubber, thermoplastic
elastomer, and ionomer resin. As the filler, although not limited
to this, for example, barium sulfate, titanium oxide, zinc oxide,
and tungsten can be used. The filler is preferably of a powder
form. As the blending amount of the filler, although not limited to
this, for example, with respect to 100 weight parts of principal
component, about 2 weight parts or more is preferable, about 5
weight parts or more is further preferable, and about 10 weight
parts or more is still more preferable. Also, the blending amount
of the filler is preferably about 1000 weight parts or less, more
preferably about 900 weight parts or less, and still more
preferably about 800 weight parts or less.
[0087] As the foaming agent, although not limited to this, for
example, azodicarbonamide, azobisisobutyronitrile,
dinitrosopentamethylenetetramine, p-toluenesulfonylhydrazide,
p,p'-oxybis (benzene sulfonyl hydrazide), and sodium hydrogen
carbonate can be used. As the blending amount of the foaming agent,
although not limited to this, for example, with respect to 100
weight parts of principal component, about 2 weight parts or more
is preferable, and about 3 weight parts or more is more preferable.
Also, the blending amount of foaming agent is preferably about 30
weight parts or less, and more preferably about 25 weight parts or
less.
[0088] The intermediate layers 20 consisting of the first and
second intermediate layers 20a and 20b may be formed so as to have
a space that is not filled with a material. Such a space, for
example, may be a concave-shaped space formed depressing a part of
layer surface, or may be a hole-shaped space penetrating the layer.
Alternatively, a space can be provided in the intermediate layers
20 by adding a foaming agent to the material of the intermediate
layers 20. As the foaming agent, the above-described foaming agent
can be used. As the blending amount of the foaming agent, although
not limited to this, for example, with respect to 100 weight parts
of principal component, about 2 weight parts or more is preferable,
and about 3 weight parts or more is more preferable. Also, the
blending amount of the foaming agent is preferably about 30 weight
parts or less, more preferably about 25 weight parts or less.
[0089] The bulk specific gravity of the cover 30 is, although not
limited to this, preferably about 0.91 or greater, and more
preferably about 0.93 or greater. Also, the bulk specific gravity
of the cover 30 is preferably about 1.5 or less, and more
preferably about 1.4 or less. As the material for the cover 30,
although not limited to this, ionomer resin, polyurethane based
thermoplastic elastomer, thermosetting polyurethane, or a mixture
of these materials can be used.
[0090] The thickness of the cover 30 is, although not limited to
this, preferably about 0.2 mm or greater, and more preferably about
0.4 mm or greater. Also, the thickness of the cover 30 is
preferably about 4 mm or less, more preferably about 3 mm or less,
and still more preferably about 2 mm or less.
[0091] On the surface of the cover 30, multiple dimples 32 are
formed. The number of dimples 32 on the entire surface of the golf
ball 1 is preferably about 200 or greater, more preferably about
250 or greater, and still more preferably about 300 or greater.
Also, the upper limit of the number of dimples 32 is preferably
about 500, more preferably about 450, still more preferably about
430, and yet still more preferably about 410. By making the number
of dimples 32 in this range, the golf ball 1 is made so that it is
easy to receive lift, and especially the carry at the time when a
driver is used can be increased.
[0092] The dimple occupancy ratio, specifically, the ratio of the
total of dimple areas defined by a planar surface edge surrounded
by the dimple edge to the ball spherical area assumed that the
dimples do not exist (the SR value) is preferably about 60% or
more, more preferably about 65% or more, and still more preferably
about 68% or more from the viewpoint of being capable of achieving
the aerodynamic characteristics sufficiently. The upper limit of
the dimple occupancy ratio is, although not limited to this,
preferably about 90%, more preferably about 85%, and still more
preferably about 80%.
[0093] The value V.sub.0 obtained by dividing the space volume of a
dimple in a flat plane surrounded by the edge of each dimple by the
volume of a column whose bottom surface is the above-described flat
plane and whose height is the maximum depth of dimple from this
bottom surface is preferably about 0.35 or greater from the
viewpoint of making the ball trajectory proper. The upper limit of
V.sub.0 is, although not limited to this, suitably about 0.80, for
example. The VR value, which is a ratio of the total volume of
dimples formed on the lower side of the flat plane surrounded by
the dimple edge to the ball spherical volume assumed that the
dimples do not exist, is preferably about 0.6% or more, more
preferably about 0.65% or more, and still more preferably about
0.7% or more. The upper limit of the VR value is preferably about
1.0%, and more preferably about 0.9%.
[0094] Multiple kinds of dimples 32 having different diameters
and/or depths can be formed. The number of kinds of dimples is
preferably 3 or more, more preferably 4 or more, and still more
preferably 5 or more. The upper limit of the number of kinds of
dimple is preferably about 20, more preferably about 15, and still
more preferably about 12. By making the number of dimple kinds in
this range, the surface occupancy ratio of dimples is made easy to
increase, so that the carry can be increased.
[0095] The shape of the dimple 32 can be made a planar circular
shape, a planar noncircular shape, or a combination of these
shapes. The average diameter of the planar circular-shaped dimple
is preferably about 2.8 mm or more, more preferably about 3.5 mm or
more, and still more preferably about 3.8 mm or more. The upper
limit of the average diameter is preferably about 5.0 mm, more
preferably about 4.6 mm, and still more preferably about 4.3 mm.
The average depth of the dimple 32 is preferably about 0.120 mm or
more, more preferably about 0.130 mm or more, and still more
preferably about 0.140 mm or more from the viewpoint of obtaining a
proper trajectory. The upper limit of the average depth is
preferably about 0.185 mm, more preferably about 0.180 mm, and
still more preferably about 0.174 mm.
[0096] The average diameter is the average value of diameters of
all the dimples, and the average depth is the average value of the
depths of all the dimples. In many cases, the golf ball is painted,
and therefore the diameter and depth of dimple are measured in a
state of being painted. The dimple diameter is measured by
measuring the width across between the points at which the land
part, which is the golf ball surface on which the dimples do not
exist, is in contact with the concave surface of dimple. Also, the
dimple depth is measured by measuring the vertical distance from
the center position of an imaginary planar circle, which is drawn
by connecting the points at which the dimple is in contact with the
land part, to the bottom surface of dimple.
[0097] The weight of the golf ball 1 is 45.93 g or less in
conformity with the golf rules, but is preferably about 45.70 g or
less. The lower limit of the weight of the golf ball 1 is not
subject to any special restriction; however, it is preferably about
44.00 g, and more preferably about 44.50 g. The diameter of the
golf ball 1 is 42.67 mm or greater in conformity with the golf
rules. The upper limit of the diameter of the golf ball 1 is not
subject to any special restriction; however, it is preferably about
43.00 mm, and more preferably about 42.80 mm.
[0098] According to the present invention, as described above, the
bulk specific gravity of a spherical zone having a radius R of 18.5
mm with the center point C of the golf ball 1 being the center is
made very small, being about 0.7 or smaller, so that the moment of
inertia of the golf ball 1 is increased. Therefore, the spin decay
rate of the golf ball during flight becomes low, so that the carry
can be increased even in the case in which the initial spin speed
is low. In FIG. 1, with the position of the radius R of 18.5 mm
from the center point C being the boundary, the first intermediate
layer 20a is disposed on the center side thereof, and the second
intermediate layer 20b is disposed on the outside thereof. However,
the present invention is not limited to this configuration. If the
bulk specific gravity of the above-described zone having the radius
R of 18.5 mm and the moment of inertia or the spin decay rate of
the golf ball 1 are within the above-described predetermined range,
the boundary line between the first intermediate layer 20a and the
second intermediate layer 20b may be arranged on the center side of
the position 18.5 mm distant from the center point C, or may be on
the outside thereof. Preferably, the boundary line is at a position
about 17.0 mm to 20.0 mm distant from the center point C. In
particular, to facilitate the optimization of ball weight, the
boundary line is preferably at the position 18.5 mm distant from
the center point C. Also, each of the first and second intermediate
layers 20a and 20b is not limited to a single layer as shown in
FIG. 1, and can be provided with a plurality of layers.
EXAMPLES
[0099] Golf balls having the configurations given in Table 1 were
prepared, and the tests for measuring the moment of inertia, the
carry, and spin speed of the golf ball, and the durability tests
were conducted. The test results are given in Table 1. The blends A
to H (wt %) of materials for the core and the first and second
intermediate layers given in Table 1 are given in Table 2. The
blends I to M (wt %) of materials for the core, the first and
second intermediate layers, and the cover are given in Table 3. In
working examples 1 to 3 and comparative examples 2 to 4, the
central portion of the core was made of a hollow structure. In
comparative example 1, the core is of a solid structure and the
intermediate layer consists of a single layer. The configuration of
this single intermediate layer was described in the column of the
second intermediate layer in Table 1 for ease of comparison. Also,
in all working examples and comparative examples, the arrangement
of dimples was made the same. Specifically, nine kinds of dimples
were used, and the number of dimples was made 336, the average
diameter of a dimple was made 4 mm, and the average depth of a
dimple was made 0.161 mm.
TABLE-US-00001 TABLE 1 Comparative Comparative Comparative
Comparative Example 1 Example 2 Example 3 Example 1 Example 2
Example 3 Example 4 Core Center Outer diameter (mm) 3.0 3.0 3.0
37.0 15.0 20.0 3.0 part Bulk specific gravity 0 0 0 1.20 0 0 0
Weight (g) 0 0 0 31.8 0 0 0 Blend -- -- -- C -- -- -- Surrounding
Outer diameter (mm) 33.0 13.0 13.0 -- 21.0 24.0 33.0 layer Bulk
specific gravity 0.45 1.30 2.00 -- 1.30 1.10 0.94 Weight (g) 8.5
1.5 2.3 -- 4.0 3.4 17.7 Blend I A B -- A D J First Outer diameter
(mm) 37.0 37.0 37.0 36.0 38.6 37.0 intermediate Bulk specific
gravity 0.94 0.45 0.45 0.94 0.94 0.94 layer Weight (g) 7.2 11.4
11.4 18.4 21.4 7.2 Blend J I I J J J Second Outer diameter (mm)
40.0 40.0 40.0 40.0 40.0 40.0 40.0 intermediate Bulk specific
gravity 2.90 3.30 3.20 0.94 1.50 3.20 1.93 layer Weight (g) 20.3
23.1 22.4 6.6 13.6 11.2 13.5 Blend E F G J K G H Cover Outer
diameter (mm) 42.7 42.7 42.7 42.7 42.7 42.7 42.7 Bulk specific
gravity 1.30 1.30 1.30 0.97 1.30 1.30 0.97 Weight (g) 9.4 9.4 9.4
7.0 9.4 9.4 7.0 Blend L L L M L L M Golf ball Weight (g) 45.4 45.4
45.5 45.4 45.5 45.4 45.4 Moments of inertia 101 101 99 80 90 97 88
BSG.sub.R.ltoreq.18.5 0.59 0.49 0.52 1.20 0.92 0.81 0.94 Durability
.largecircle. .largecircle. .largecircle. .largecircle. X X
.largecircle. Distance (m) 8 deg 1.3 1.3 1.2 -- 0.6 1.1 0.4 11 deg
1.5 1.4 1.3 -- 0.7 1.2 0.5 Spin decay rate [%] 2.5 2.5 2.6 3.3 2.9
2.7 3.0
TABLE-US-00002 TABLE 2 A B C D E F G H BR730 100 100 100 100 100
100 100 100 Dicumyl 1 1 1 1 1 1 1 1 peroxide Zinc oxide 40.9 178.4
24.8 4.6 463.9 1226.1 557.6 16.3. Nocrac 0.1 0.1 0.1 0.1 0.1 0.1
0.1 0.1 NS-6 Zinc 20.0 20.0 20.0 5.0 25.5 20.0 36.0 25.5 acrylate
Tungsten -- -- -- 10.0 -- -- 36.4 --
[0100] BR730 is the trade name of 1,4-cis-polybutadiene available
from JSR Corporation, which was used as the base rubber.
[0101] Dicumyl peroxide is available from NOF Corporation, which
was used as the initiator.
[0102] Zinc oxide is available from Sakai Chemical Industry Co.,
Ltd.
[0103] Nocrac NS-6 is the trade name of
2-2'-methylenebis(4-methyl-6-t-butylphenol) available from Ouchi
Shinko Chemical Industry Co., Ltd., which was used as an
antioxidant.
[0104] Zinc acrylate is available from Nihon Jyoryu Kogyo Co.,
Ltd.
[0105] Tungsten is available from Nippon Tungsten Co., Ltd. (in
powder form).
TABLE-US-00003 TABLE 3 I J K L M Dynaron 6100P -- 32 -- -- --
Polytail H -- 2 -- -- -- Behenic acid -- 18 -- -- -- Calcium
hydroxide -- 2.3 -- -- -- Foaming agent 4 -- -- -- --
Trimethylolpropane 1.1 -- -- -- -- Himilan 1706 35 -- -- -- --
Himilan 1557 15 -- 75 75 75 Himilan 1605 50 66 -- -- -- Himilan
1855 -- -- 25 25 25 Magnesium stearate -- -- 1.8 1.8 1.8 Titanium
oxide -- -- 3.8 3.8 3.8 Barium sulfate 300 -- -- 77.2 48.1 --
[0106] Dynaron 6100P is the trade name of a hydrogenated
thermoplastic elastomer available from JSR Corporation.
[0107] Polytail H is the trade name of polyolefin polyol available
from Mitsubishi Chemical Corporation.
[0108] Behenic acid is available from NOF Corporation.
[0109] Calcium hydroxide is available from Shiraishi Kogyo Kaisha
Ltd.
[0110] The foaming agent is the ADCA master batch available from
Otsuka Chemical Co., Ltd.
[0111] Himilan 1706 is the trade name of an ionomer resin available
from DuPont-Mitsui Polychemicals Co., Ltd.
[0112] Himilan 1557 is the trade name of an ionomer resin available
from DuPont-Mitsui Polychemicals Co., Ltd.
[0113] Himilan 1605 is the trade name of an ionomer resin available
from DuPont-Mitsui Polychemicals Co., Ltd.
[0114] Himilan 1855 is the trade name of an ionomer resin available
from DuPont-Mitsui Polychemicals Co., Ltd.
[0115] Barium sulfate 300 is available from Sakai Chemical Industry
Co., Ltd.
[0116] The moment of inertia of the golf ball was measured by using
a measuring instrument for moment of inertia (M01-005 available
from Inertia Dynamics Inc.). This measuring instrument calculates
the moment of inertia of a golf ball from a difference between the
vibration period at the time when the golf ball is placed on a jig
of the measuring instrument and the vibration period at the time
when the golf ball is not placed thereon.
[0117] The durability of the golf ball was evaluated by using an
ADC Ball COR Durability Tester available from Automated Design
Corporation in U.S.A. This tester has the function of discharging a
golf ball by using a pneumatic pressure and thereafter causing the
golf ball to collide continuously with two metal plates disposed in
parallel with each other. The test results were evaluated as in
Table 1 so that a circle mark indicates that the number of
discharges required until the ball is broken is 30 or more, a
triangle mark indicates that the number of discharges is less than
30 and not less than 20, and a cross mark indicates that the number
of discharges is less than 20. As the measurement conditions, the
incidence velocity of the ball was made 43 m/s.
[0118] The carry of the golf ball was tested by using a launcher
(UBL available from Automated Design Corporation) under the
conditions that the ball initial velocity was 59 m/s, the initial
spin speed was 2000 rpm, and the delivery angles were 8 degrees and
11 degrees. The result of carry test in Table 1 is shown by the
increased distance (m) of each example with the carry of
comparative example 1 being the reference. The UBL is a device in
which two pairs of drums are installed vertically, and belts are
set around the upper two drums and the lower two drums, the drums
are rotated and a ball is inserted therebetween, whereby the ball
is launched under desirable conditions.
[0119] The spin speed of the golf ball during flight with respect
to time was measured by using a golf ball trajectory tracking
system (TrackMan available from TrackMan A/S). From these
measurement data, the gradient of an approximated straight line was
calculated by the least-squares method, and the spin loss per one
second of the golf ball was determined. The spin decay rate was
defined as a value obtained by dividing the spin loss per one
second by the initial spin speed.
[0120] As shown in Table 1, as compared with the golf ball of
comparative example 1 of a conventional construction provided with
a solid core having an outside diameter of 37 mm and a bulk
specific gravity of 1.20, an intermediate layer having an outside
diameter of 40 mm and a bulk specific gravity of 0.94, and a cover
having an outside diameter of 42.7 mm and a bulk specific gravity
of 0.97, in working example 1, the core has a hollow part having an
outside diameter of 3.0 mm, the surrounding layer having an outside
diameter of 33.0 mm has a bulk specific gravity of 0.45, and the
first intermediate layer having an outside diameter of 37 mm has a
bulk specific gravity of 0.94. Thereby, the bulk specific gravity
of the spherical zone having a radius R of 18.5 mm (hereinafter,
referred to as the "BSG.sub.R.ltoreq.18.5") could be decreased
significantly from 1.20 to 0.59. Also, since the bulk specific
gravity of the second intermediate layer having an outside diameter
of 40 mm was made 2.90, the moment of inertia could be increased
greatly from 80 gcm.sup.2 to 100 gcm.sup.2. As a result, the spin
decay rate of working example 1 decreased to 2.5% as compared with
3.3% of comparative example 1, and also the carry increased by 1.3
to 1.5 m as compared with comparative example 1.
[0121] For the golf ball of working example 2, in which as compared
with working example 1, the outside diameter of the surrounding
layer is decreased to 13.0 mm, the bulk specific gravity of the
surrounding layer is increased to 1.30 and, on the other hand, the
bulk specific gravity of the first intermediate layer is decreased
to 0.45, and the bulk specific gravity of the second intermediate
layer is increased to 3.30, the BSG.sub.R.ltoreq.18.5 could be
decreased to 0.49, and the moment of inertia could be increased to
101 gcm.sup.2. As a result, the spin decay rate of working example
2 decreased to 2.5% as compared with 3.3% of comparative example 1,
and also the carry increased by 1.3 to 1.4 m as compared with
comparative example 1.
[0122] For the golf ball of working example 3, in which bulk
specific gravity of the surrounding layer is more increased to 2.00
and, on the other hand, the bulk specific gravity of the second
intermediate layer is slightly decreased to 3.20, the
BSG.sub.R.ltoreq.18.5 could be decreased to 0.52, and the moment of
inertia could be increased to 99 gcm.sup.2. As a result, the spin
decay rate of working example 3 decreased to 2.6% as compared with
3.3% of comparative example 1, and also the carry increased by 1.2
to 1.3 m as compared with comparative example 1.
[0123] For the golf ball of comparative example 2, in which as
compared with working example 1, the outside diameter of the hollow
part is increased to 15.0 mm, the outside diameter of the
surrounding layer is decreased to 21.0 mm, the bulk specific
gravity of the surrounding layer is increased to 1.30, the outside
diameter of the first intermediate layer is slightly decreased to
36.0 mm, and the bulk specific gravity of the second intermediate
layer is decreased to 1.50, although the BSG.sub.R.ltoreq.18.5 was
0.92, being smaller than that of comparative example 1, it was far
larger than those of working examples 1 to 3. Also, although the
moment of inertia was 90 gcm.sup.2, being higher than that of
comparative example 1, it was lower than those of working examples
1 to 3. As a result, the spin decay rate of comparative example 2
was as high as 2.9%, and the carry increased merely by 0.6 to 0.7
as compared with comparative example 1. Also, the golf ball of
comparative example 2 has a problem of poor durability because the
outside diameter of the hollow part thereof is large.
[0124] For the golf ball of comparative example 3, in which as
compared with comparative example 2, the outside diameter of the
hollow part is more increased to 20.0 mm, the outside diameter of
the surrounding layer is increased to 24.0 mm, the bulk specific
gravity of the surrounding layer is decreased to 1.10, the outside
diameter of the first intermediate layer is increased to 38.6 mm,
and the bulk specific gravity of the second intermediate layer is
significantly increased to 3.20, although the BSG.sub.R.ltoreq.18.5
was 0.81, being smaller than that of comparative example 2, it was
still larger than those of working examples 1 to 3. Although the
moment of inertia of the golf ball of comparative example 3 was as
high as 97 gcm.sup.2, the spin decay rate thereof was as low as
2.7%, and the carry thereof also increased by 1.1 to 1.2 m as
compared with comparative example 1, the golf ball of comparative
example 3 has a problem of poor durability because the outside
diameter of the hollow part thereof is large.
[0125] For the golf ball of comparative example 4, in which as
compared with working example 1, the bulk specific gravity of the
surrounding layer is increased to 0.94 and, on the other hand, the
bulk specific gravity of the second intermediate layer is decreased
to 1.93, and the bulk specific gravity of the cover is decreased to
0.97, although the BSG.sub.R.ltoreq.18.5 was 0.94, being smaller
than that of comparative example 1, it was still larger than those
of working examples 1 to 3. Also, although the moment of inertia
was 88 gcm.sup.2, being higher than that of comparative example 1,
it was lower than those of working examples 1 to 3. As a result,
the spin speed of comparative example 4 is as high as 3.0%, and the
carry is also increased merely by 0.4 to 0.5 as compared with
comparative example 1.
* * * * *