U.S. patent application number 11/493541 was filed with the patent office on 2008-01-31 for golf ball.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. Invention is credited to Toshihiko Manami, Eiji Takehana.
Application Number | 20080026873 11/493541 |
Document ID | / |
Family ID | 38987009 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080026873 |
Kind Code |
A1 |
Manami; Toshihiko ; et
al. |
January 31, 2008 |
Golf ball
Abstract
The invention provides a golf ball having a core and a cover of
one or more layer, wherein at least one layer of the cover is made
of a material obtained by molding a mixture of (a) a metal ion
neutralization product of an olefin-unsaturated carboxylic acid
random copolymer having a Shore D hardness of at least 60; (b) an
unsaturated fatty acid; and (c) a basic inorganic metal compound
capable of neutralizing acid groups in components (a) and (b). The
golf ball has both a good feel on impact and excellent scuff
resistance while retaining a good flight performance.
Inventors: |
Manami; Toshihiko;
(Chichibu-shi, JP) ; Takehana; Eiji;
(Chichibu-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
|
Family ID: |
38987009 |
Appl. No.: |
11/493541 |
Filed: |
July 27, 2006 |
Current U.S.
Class: |
473/373 ;
473/374; 473/378 |
Current CPC
Class: |
A63B 37/0023 20130101;
A63B 37/0031 20130101; C08L 23/0876 20130101; A63B 37/0003
20130101 |
Class at
Publication: |
473/373 ;
473/374; 473/378 |
International
Class: |
A63B 37/04 20060101
A63B037/04; A63B 37/06 20060101 A63B037/06; A63B 37/14 20060101
A63B037/14 |
Claims
1. A golf ball comprising a core and a cover of one or more layer,
wherein at least one layer of the cover is made of a material
obtained by molding a mixture comprising: (a) 100 parts by weight
of a binary polymer which is a metal ion neutralization product of
an olefin-unsaturated carboxylic acid random copolymer having a
Shore D hardness of at least 60; (b) 5 to 60 parts by weight of an
unsaturated fatty acid; (c) 1 to 10 parts by weight of a basic
inorganic metal compound capable of neutralizing acid groups in
components (a) and (b); and wherein said material does not comprise
a ternary polymer.
2. The golf ball of claim 1, wherein an outermost layer of the
cover is made of the material obtained by molding the mixture
comprising components (a) to (c).
3. The golf ball of claim 1, wherein the mixture has a melt mass
flow rate of at least 3.8 to 6.9 g/10 min.
4. The golf ball of claim 1, wherein the unsaturated fatty acid (b)
is elaidic acid and/or erucic acid.
5. The golf ball of claim 1, wherein the basic inorganic metal
compound (c) is calcium hydroxide.
6. The golf ball of claim 1, wherein the cover has a Shore D
hardness of from 46 to 58.
7. The golf ball of claim 1, wherein the metal ion neutralization
product of an olefin-unsaturated carboxylic acid randon copolymer
serving as component (a) has a Shore D hardness of at least 62.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a golf ball having a core
and cover of one or more layer. More specifically, the invention
relates to a golf ball having both a good feel on impact and
excellent scuff resistance while retaining a good flight
performance.
[0002] In recent years, ionomer resins have been widely used in
golf ball cover materials. Ionomer resins are ionic copolymers of
an olefin such as ethylene with an unsaturated carboxylic acid such
as acrylic acid, methacrylic acid or maleic acid, in which some of
the acidic groups are neutralized with metal ions such as sodium,
lithium, zinc or magnesium. In particular, ionomer resins have
excellent characteristics such as durability and rebound
resilience, and are thus well-suited for use as the base resin in a
golf ball cover material.
[0003] Ionomer resins account for most of the cover material resin
in use today, and enable the production of golf balls endowed with
the above properties. Yet, golfers are always on the lookout for
golf balls having a high rebound resilience and excellent flight
characteristics. Examples of such improvements include the use of
terpolymers obtained by copolymerizing a third component such as an
alkyl acrylate with ethylene and an unsaturated carboxylic acid, as
described in U.S. Pat. No. 6,653,382 and U.S. Pat. No. 6,815,480.
However, the admixture of oleic acid with this terpolymer makes the
resulting material too soft for use in golf balls, leading to such
undesirable effects as a low ball initial velocity and a poor scuff
resistance.
[0004] U.S. Pat. No. 6,762,246 teaches a material obtained by
mixing a low-molecular-weight compound such as a wax with a ternary
ionomer, but the overall performance of golf balls thereby obtained
tends to decline.
[0005] Given the importance placed on the feel of the ball when
played, the use of a low-hardness ionomer in the cover material has
also been proposed. However, when a low-hardness ionomer is used,
the initial velocity of the ball tends to decline and the scuff
resistance tends to worsen.
SUMMARY OF THE INVENTION
[0006] It is therefore an object of the invention to provide a golf
ball which, in addition to exhibiting an excellent flight
performance, also has a more than satisfactory feel on impact and
scuff resistance.
[0007] The inventors have conducted extensive investigations, as a
result of which they have discovered that, in a golf ball having a
core and a cover of one or more layer, when at least one layer of
the cover is made of a material obtained by using (a) a metal ion
neutralization product of an olefin-unsaturated carboxylic acid
random copolymer having a Shore D hardness of at least 60, (b) an
unsaturated fatty acid, and (c) a basic inorganic metal compound
capable of neutralizing acid groups in foregoing components (a) and
(b), and mixing and molding these components (a) to (c) in specific
proportions, the ball can be imparted with both a good feel and an
excellent scuff resistance while retaining a good rebound
resilience.
[0008] Accordingly, the invention provides the following golf
balls. [0009] [1] A golf ball comprising a core and a cover of one
or more layer, wherein at least one layer of the cover is made of a
material obtained by molding a mixture comprising:
[0010] (a) 100 parts by weight of a metal ion neutralization
product of an olefin-unsaturated carboxylic acid random copolymer
having a Shore D hardness of at least 60;
[0011] (b) 5 to 60 parts by weight of an unsaturated fatty acid;
and
[0012] (c) 1 to 10 parts by weight of a basic inorganic metal
compound capable of neutralizing acid groups in components (a) and
(b). [0013] [2] The golf ball of [1], wherein an outermost layer of
the cover is made of the material obtained by molding the mixture
comprising components (a) to (c). [0014] [3] The golf ball of [1],
wherein the mixture has a melt mass flow rate of at least 2.0 g/10
min. [0015] [4] The golf ball of [1], wherein the unsaturated fatty
acid (b) is at least one selected from the group consisting of
oleic acid, elaidic acid, erucic acid, linoleic acid and linolenic
acid. [0016] [5] The golf ball of [1], wherein the basic inorganic
metal compound (c) is calcium hydroxide.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The invention is described more fully below.
[0018] The golf ball of the invention has a core and a cover of one
or more layer. The core is not limited to one layer, and may, if
necessary, be composed of two or more layers.
[0019] A rubber composition obtained by a conventional method and
controlled vulcanization conditions, ingredient proportions and the
like may be used as the core material. The core formulation
generally includes such ingredients as a base rubber, crosslinking
agent, co-crosslinking agent and inert filler. Natural rubbers
and/or synthetic rubbers hitherto used in solid golf balls may be
employed as the base rubber. For example, 1,4-polybutadiene having
a cis structure content of at least 40% may be used. If desired,
other types of rubber, such as natural rubber, polyisoprene rubber
or styrene-butadiene rubber may be suitably blended with the
polybutadiene. The crosslinking agent is exemplified by organic
peroxides such as dicumyl peroxide and di-t-butyl peroxide. The
co-crosslinking agent is not subject to any particular limitation.
Illustrative examples include the metal salts of unsaturated fatty
acids, particularly the zinc salts and magnesium salts of
unsaturated fatty acids having 3 to 8 carbon atoms (e.g., acrylic
acid, methacrylic acid). Examples of inert fillers include zinc
oxide, barium sulfate, silica, calcium carbonate and zinc
carbonate. Aside from the foregoing rubber composition, use may be
made of a thermoplastic resin or thermoplastic elastomer, such as
an ionomer resin or a polyester elastomer, as the solid core
material.
[0020] The solid core may be produced by using a known process to
cure/vulcanize a rubber composition containing the various above
ingredients. For example, core production may involve masticating
the ingredients using a mixing apparatus such as a Banbury mixer or
roll mill, compression molding or injection molding the masticated
material in a core mold, then curing the molded body by suitably
heating at a temperature sufficient for the peroxide and
co-crosslinking agent to act. To illustrate, when dicumyl peroxide
is used as the peroxide and zinc acrylate is used as the
co-crosslinking agent, heating is typically carried out at from 130
to 170.degree. C., and preferably 150 to 160.degree. C., for a
period of 10 to 40 minutes, and preferably 12 to 20 minutes.
[0021] The hardness of the solid core is not subject to any
particular limitation and may be adjusted as appropriate. The core
may have a hardness distribution such that the hardness is
substantially the same from the center to the surface of the core,
or the core may have a hardness difference between the center and
surface thereof.
[0022] It is desirable for the solid core to have a diameter of at
least 25 mm, and preferably at least 36 mm, but not more than 42
mm, and preferably not more than 24 mm. The core weight is
preferably from 20 to 32 g, and more preferably from 27 to 30
g.
[0023] In the present invention, at least one layer of the cover of
one or more layers is made of a material obtained by molding a
mixture composed of the following essential ingredients:
[0024] (a) 100 parts by weight of a metal ion neutralization
product of an olefin-unsaturated carboxylic acid random
copolymer;
[0025] (b) 5 to 60 parts by weight of an unsaturated fatty acid;
and
[0026] (c) 1 to 10 parts by weight of a basic inorganic metal
compound capable of neutralizing acid groups in components (a) and
(b).
[0027] The olefin in component (a) is generally one having at least
2 carbons, but not more than 8 carbons, and preferably not more
than 6 carbons. Illustrative examples include ethylene, propylene,
butene, pentene, hexene, heptene and octene. Ethylene is especially
preferred.
[0028] Examples of the unsaturated carboxylic acid include acrylic
acid, methacrylic acid, maleic acid and fumaric acid. Acrylic acid
and methacrylic acid are preferred.
[0029] The random copolymer of the random copolymer metal salt used
as component (a) may be obtained by random copolymerization of the
above-mentioned ingredients according to a known method. It is
recommended that the content of unsaturated carboxylic acid (acid
content) included in the random copolymer be generally at least 2
wt % (here and below, "wt %" stands for percent by weight),
preferably at least 6 wt %, and more preferably at least 8 wt %,
but not more than 25 wt %, preferably not more than 20 wt %, and
more preferably not more than 15 wt %. If the acid content is too
low, the rebound resilience may decrease. On the other hand, if the
acid content is too high, the processability may decrease.
[0030] The metal ion neutralization product of a random copolymer
used as component (a) may be obtained by neutralizing some of the
acid groups on the random copolymer with metal ions. Illustrative
examples of metal ions for neutralizing the acid groups include
Na.sup.+, K.sup.+, Li.sup.+, Zn.sup.++, Cu.sup.++, Mg.sup.++,
Ca.sup.++, Co.sup.++, Ni.sup.++ and Pb.sup.++. Of these, Na.sup.+,
Li.sup.+, Zn.sup.++ and Mg.sup.++ are preferred, and Zn.sup.++ is
especially recommended. The degree to which the random copolymer is
neutralized by these metal ions is not subject to any particular
limitation. The neutralization product may be obtained by a known
method, such as one that involves introducing to the random
copolymer a suitable compound, examples of which include formates,
acetates, nitrates, carbonates, bicarbonates, oxides, hydroxides
and alkoxides of the above metal ions.
[0031] In the inventive golf ball, a binary polymer which is a
metal ion neutralization product of an olefin-unsaturated
carboxylic acid random copolymer is used in this way as component
(a). The reason is that, while using the subsequently described
unsaturated fatty acid with the above metal ion neutralization
product of a binary copolymer serving as component (a) is essential
for imparting the inventive ball with a soft feel and an excellent
scuff resistance, a binary polymer better plasticizes the overall
cover material than does a ternary polymer, enabling a good
moldability to be maintained.
[0032] It is critical that the metal ion neutralization product of
an olefin-unsaturated carboxylic acid random copolymer serving as
component (a) have a Shore D hardness of at least 60, preferably at
least 61, and more preferably at least 62. Given that component (a)
serves as the base resin of the cover material, and that the
material hardness of the base resin is largely responsible for the
hardness, durability and scuff resistance of the ball, it is
essential to set the Shore D hardness of component (a) within the
foregoing range.
[0033] Illustrative examples of the metal salt of a random
copolymer serving as component (a) include Himilan 1605, Himilan
1706, Himilan AM7317, Himilan AM7318 and Himilan AM7315 (all
products of DuPont-Mitsui Polychemicals Co., Ltd.), and Surlyn
7930, Surlyn 8150, Surlyn 8220 and Surlyn 9150 (all products of
E.I. DuPont de Nemours & Co.).
[0034] In the invention, the unsaturated fatty acid used as
component (b) generally has one or more double bond on the
molecule. Illustrative examples include those having one double
bond, such as oleic acid (18 carbons), elaidic acid (the trans
isomer of oleic acid) and erucic acid (22 carbons); those having
two double bonds, such as linoleic acid (18 carbons); and those
having three double bonds, such as linolenic acid. These may be
used singly or as combinations of two or more. The use of oleic
acid is especially preferred.
[0035] Above component (b) is included in an amount, per 100 parts
by weight of component (a), of at least 5 parts by weight,
preferably at least 8 parts by weight, and more preferably at least
10 parts by weight. Use in a smaller amount will prevent the
hardness of the ionomer resin from being lowered to the desired
level. The upper limit in the amount of component (b) is 60 parts
by weight or less, preferably 50 parts by weight or less, and more
preferably 40 parts by weight or less. At an amount greater than
this upper limit, uptake by the resin becomes difficult and
bleeding tends to arise.
[0036] The golf ball material of the invention includes as
component (c) a basic inorganic metal compound capable of
neutralizing acid groups on above components (a) and (b). It
neutralizes un-neutralized carboxyl groups within the ionomer resin
and carboxyl groups in component (b), thereby forming a metal salt.
This results in strong crosslinkages, enhancing the scuff
resistance.
[0037] In the golf ball of the invention, as noted above, an
unsaturated fatty acid is included as component (b). The amount of
component (b) is relatively small, which should help avoid problems
such as molding defects.
[0038] The reason for using an unsaturated fatty acid having one or
more double bond on the molecule is that the ionomer resin
hardness-lowering effect is much larger than that of saturated
fatty acids having no double bonds (e.g., stearic acid (18
carbons)).
[0039] Component (c) of the invention is a basic inorganic metal
compound capable of neutralizing acid groups in above components
(a) and (b), thus enabling the rebound resilience and
processability to be freely controlled.
[0040] Illustrative examples of the metal ions used in the basic
inorganic metal compound include Li.sup.+, Na.sup.+, K.sup.+,
Ca.sup.++, Mg.sup.++, Zn.sup.++, Al.sup.+++, Ni.sup.+, Fe.sup.++,
Fe.sup.+++, Cu.sup.++, Mn.sup.++, Sn.sup.++, Pb.sup.++ and
Co.sup.++. Basic inorganic fillers containing these metal ions may
be used as the inorganic metal compound. Specific examples include
magnesium oxide, magnesium hydroxide, magnesium carbonate, zinc
oxide, sodium hydroxide, sodium carbonate, calcium oxide, calcium
hydroxide, lithium hydroxide and lithium carbonate. The use of
calcium hydroxide, which has a high reactivity with the ionomer
resin, is especially preferred.
[0041] Above component (c) is included in an amount, per 100 parts
by weight of component (a), of at least 1 part by weight,
preferably at least 1.2 parts by weight, and more preferably at
least 1.5 parts by weight. Below this amount, the degree of
neutralization falls shorts and a sufficient rebound resilience
cannot be achieved. The upper limit in the amount of component (c)
per 100 parts by weight of component (a) is not more than 10 parts
by weight, preferably not more than 7 parts by weight, and more
preferably not more than 6 parts by weight.
[0042] Other materials may be suitably included in the mixture of
components (a) to (c), although it is recommended that the mixture
have a melt mass flow rate (measured in accordance with JIS-K7210
at a test temperature of 190.degree. C. and under a test load of 21
N (2.16 kgf)) of preferably at least 2.0 g/10 min, and more
preferably at least 2.5 g/10 min, but preferably not more than 6
g/10 min, and more preferably not more than 5 g/10 min. If the melt
mass flow rate of the hot mixture is too low, the processability
will markedly decline.
[0043] Various additives may be optionally included in the mixture.
For example, when the mixture is to be used as a cover material,
additives such as pigments, dispersants, antioxidants, ultraviolet
absorbers and light stabilizers may be included therein. Moreover,
to improve the feel of the ball on impact, in addition to the above
essential ingredients, various non-ionomeric thermoplastic
elastomers may be included in the material of the invention.
Examples of such non-ionomeric thermoplastic elastomers include
olefin elastomers, styrene elastomers, ester elastomers, and
urethane elastomers. The use of olefin elastomers and styrene
elastomers is especially preferred.
[0044] The mixing method used to obtain the above mixture is not
subject to any particular limitation. For example, mixture may be
carried out at a heating temperature of from 150 to 250.degree. C.
using as the mixing apparatus an internal mixer such as a
kneading-type twin-screw extruder, a Banbury mixer or a kneader. No
limitation is place on the method of incorporating the various
additives other than above essential ingredients (a) to (c).
Examples include a method in which the additives are compounded
with the above essential ingredients and simultaneously mixed under
applied heat, and a method in which the essential ingredients are
first mixed under heating, then the optional additives are added,
following by additional mixing under applied heat. In particular,
when a co-rotating twin-screw extruder is used, the unsaturated
fatty acid may be injected from various vent ports on the
twin-screw extruder using a plunger-type pump. The basic inorganic
metal compound may be added from any desired point using a side
feed.
[0045] To obtain the cover in the invention, use may be made of a
method which involves placing within a mold a single-layer core or
a multi-layer core of two or more layers that has been
pre-fabricated according to the type of ball, mixing and melting
the above mixture under applied heat, and injection-molding the
molten mixture so as to encase the core within the desired cover.
In this way, the cover-forming operation can be carried out in a
state that ensures an outstanding heat stability, flow and
moldability, enabling the golf ball ultimately obtained to have a
high rebound resilience and also a good feel on impact and
excellent scuff resistance. Alternatively, the method used to form
the cover may be one in which first a pair of hemispherical
half-cups is molded from the cover material of the invention,
following which the half-cups are placed over a core and molded
under pressure at 120 to 170.degree. C. for 1 to 5 minutes.
[0046] In the practice of the invention, the cover is not limited
to one layer only, and may instead be formed with a multilayer
structure of two or more layers. If the cover has one layer, the
thickness is preferably from 0.5 to 3 mm. If the cover has two
layers, it is preferable for the outer cover layer to have a
thickness in a range of 0.5 to 2.0 mm and for the inner cover layer
to have a thickness in a range of 0.5 to 2.0 mm. When the cover has
a multilayer structure, the cover material of the invention may be
used either at the inner side of the multilayer structure or in the
outermost layer cover. However, in the present invention, use as
the outermost layer is preferred. That is, when the cover is formed
of two or more layers, to obtain a good feel and to make the scuff
resistance even better, it is advantageous for a molded material
obtained from the mixture containing above components (a) to (c) to
be used as the chief material of the outermost layer.
[0047] With regard to the cover hardness, it is desirable for the
respective layers making up the cover (cover layers) to have a
Shore D hardness of at least 40, and preferably at least 45, but
not more than 60, and preferably not more than 58.
[0048] The surface of the outermost layer of the cover may have a
plurality of dimples formed thereon, and the cover may be
administered various treatment, such as surface preparation,
stamping and painting. In particular, the ease of operation
involved in administering such surface treatment to a golf ball
cover made of the cover material of the invention can be improved
on account of the good moldability of the cover surface.
[0049] The present invention provides a golf ball in which a
material obtained by molding the above mixture is used in at least
one cover layer. The type of golf ball is not subject to any
particular limitation, provided the ball has a core and at least
one cover layer. Exemplary golf balls include solid golf balls,
such as two-piece golf balls having a solid core encased by a cover
and multi-piece golf balls with three or more layers (e.g.,
three-piece solid golf balls); and thread-wound golf balls having a
thread-wound core encased by a cover of one layer or having a
multilayer structure of two or more layers.
[0050] The golf ball of the invention, which can be manufactured so
as to conform with the Rules of Golf for competitive play, may be
produced to a ball diameter of not less than 42.67 mm and a weight
of not more than 45.93 g. The golf ball of the invention may be
suitably used in all competitive play, whether by amateur golfers
having a head speed of 30 to 40 m/s or by professional golfers
having a head speed of 45 m/s.
[0051] As described above, the golf ball of the invention provides
both a good feel on impact and an excellent scuff resistance while
retaining a good flight performance.
EXAMPLES
[0052] Examples of the invention and Comparative Examples are given
below by way of illustration, and not by way of limitation.
Examples 1 to 6, Comparative Examples 1 to 4
[0053] Using a core material composed primarily of the
polybutadiene shown in Table 1 below, a solid core with a diameter
of 35.3 mm, a weight of 27.1 g, and a deflection under 100 kg of
loading of 4.0 mm was produced. The deflection was the measured
amount of deformation by the core when compressed under a final
load of 1,275 N (130 kgf) from an initial load of 98 N (10
kgf).
TABLE-US-00001 TABLE 1 Amount (pbw) Core Polybutadiene (1) 50
formulation Polybutadiene (2) 50 Zinc acrylate 24.0 Peroxide (1)
0.6 Peroxide (2) 0.6 Antioxidant 0.1 Zinc salt of
pentachlorothiophenol 0.1 Zinc oxide 5 Barium sulfate 20.8 Core
Diameter (mm) 35.3 properties Weight (g) 27.1 Deflection (mm)
4.0
[0054] Details of the above formulation are provided below. [0055]
Butadiene rubber (1): BR01 (trade name), available from JSR
Corporation. [0056] Butadiene rubber (2): BR51 (trade name), a
grade of BR730 having improved extrudability available from JSR
Corporation. [0057] Peroxide (1): Dicumyl peroxide, available from
NOF Corporation under the trade name Percumyl D. [0058] Peroxide
(2): 1,1-Bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, available
from NOF Corporation under the trade name Perhexa 3M-40. [0059]
Antioxidant: Nocrac NS-6 (trade name), available from Ouchi Shinko
Chemical Industry Co., Ltd.
[0060] Next, an intermediate layer material of the composition
shown in Table 2 was injection-molded to a thickness of 1.65 mm in
a mold within which the above solid core had been placed. The cover
material was then mixed in a co-rotating twin-screw extruder (screw
diameter, 32 mm; L/D=32; motor capacity, 7.5 kw; with vacuum vent)
at 200.degree. C. The resulting mixture was injected into a mold
within which the intermediate layer material-covered core had been
placed, and injection-molded to a cover thickness of 2.05 mm,
thereby producing a three-piece solid golf ball having a diameter
of 42.7 mm. The surface of the golf ball obtained in each example
was coated with a non-yellowing urethane resin-based paint. The
properties (initial velocity, feel on impact, scuff resistance,
etc.) of the golf balls obtained in each example were evaluated as
described below. The results are presented in Table 2.
TABLE-US-00002 TABLE 2 Example Comparative Example 1 2 3 4 5 6 1 2
3 4 Intermediate layer Hytrel 4047 100 100 100 100 100 100 100 100
100 100 formulation (pbw) Intermediate Material hardness 40 40 40
40 40 40 40 40 40 40 layer (Shore D) properties Specific gravity
1.12 1.12 1.12 1.12 1.12 1.12 1.12 1.12 1.12 1.12 Sphere composed
of Outside diameter 38.6 38.6 38.6 38.6 38.6 38.6 38.6 38.6 38.6
38.6 core covered by (mm) intermediate layer Cover Component
Himilan 100 100 100 100 50 formulation (a) 1706 (pbw) Himilan 100
100 100 100 50 1605 Himilan 50 1601 Himilan 50 1557 Component Oleic
20 30 40 20 30 40 (b) acid Component Calcium 1.83 3.41 5.2 3.03
4.92 5 (c) hydroxide Titanium 4 4 4 4 4 4 4 4 4 4 dioxide Magnesium
2 2 2 2 stearate Blue 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05
0.05 pigment Cover Melt mass flow 4.0 4.3 5.9 3.8 4.8 6.9 1.3 2.9
1.7 2.1 properties rate (g/10 min) Cover hardness 50 50 46 58 56 54
62 63 63 60 (Shore D) Specific gravity 1.00 1.00 0.99 0.98 0.97
0.99 0.99 0.97 0.98 0.97 Ball Diameter (mm) 42.7 42.7 42.7 42.7
42.7 42.7 42.7 42.7 42.7 42.7 properties Weight (g) 45.4 45.4 45.4
45.3 45.1 45.4 45.3 45.1 45.2 45.1 Deflection (mm) 3.4 3.4 3.4 3.2
3.2 3.3 3.1 3.0 3.0 3.2 Initial velocity 76.1 76.3 76.4 77.1 77.1
76.9 76.9 77.3 77.5 77.0 (m/s) Scuff resistance 4.4 4.4 4.3 4.3 4.2
4.1 4.6 4.1 4.2 3.7 (rating) Feel on impact good good good good
good good poor poor poor poor
[0061] Details of the above formulation are provided below. [0062]
(I) Hytrel 4047 (trade name): [0063] Thermoplastic polyether ester
elastomer available from DuPont-Toray Co., Ltd. (Shore D hardness,
40). [0064] (II) Himilan 1706 (trade name): [0065] Ionomer resin of
ethylene-methacrylic acid copolymer neutralized with zinc ions,
available from DuPont-Mitsui Polychemicals Co., Ltd. (Shore D
hardness, 64). [0066] (III) Himilan 1605 (trade name): [0067]
Ionomer resin of ethylene-methacrylic acid copolymer neutralized
with sodium ions, available from DuPont-Mitsui Polychemicals Co.,
Ltd. (Shore D hardness, 65). [0068] (IV) Himilan 1601 (trade name):
[0069] Ionomer resin of ethylene-methacrylic acid copolymer
neutralized with sodium ions, available from DuPont-Mitsui
Polychemicals Co., Ltd. (Shore D hardness, 59). [0070] (V) Himilan
1557 (trade name): [0071] Ionomer resin of ethylene-methacrylic
acid copolymer neutralized with zinc ions, available from
DuPont-Mitsui Polychemicals Co., Ltd. (Shore D hardness, 59).
[0072] (VI) Oleic acid: [0073] NAA-300 (trade name), available from
NOF Corporation. [0074] (VII) Magnesium stearate: [0075] Nissan
Magnesium Stearate (trade name), available from NOF Corporation.
[0076] (VIII) Titanium oxide: [0077] Tipaque R550 (trade name),
available from Ishihara Sangyo Kaisha, Ltd. [0078] (IX) Blue
pigment: [0079] Ultramarine Blue EP-62 (trade name), available from
Holliday Pigments. [0080] (X) Calcium hydroxide: [0081] CLS-B
(trade name), available from Shiraishi Kogyo.
[0082] [Evaluation of Cover Material Properties]
Melt Mass Flow Rate
[0083] The melt mass flow rate (or melt index) of the material, as
measured in accordance with JIS-K7210 (test temperature,
190.degree. C.; test load, 21 N (2.16 kgf).
Material Hardnesses of Intermediate Layer and Cover Resin
[0084] The Shore D hardnesses measured according to ASTM D-2240 are
shown.
[0085] [Evaluation of Ball Properties]
Ball Deflection (mm)
[0086] The amount of deformation (mm) by the golf ball when
compressed under a final load of 1,275 N (130 kgf) from an initial
load state of 98 N (10 kgf) was determined.
Initial Velocity of Ball (m/s)
[0087] The initial velocity (m/s) was measured using an initial
velocity measuring apparatus of the same type as that of the
official golf ball regulating-body--R&A (USGA), and in
accordance with R&A (USGA) rules.
Feel on Impact
[0088] Sensory evaluations were carried out with a panel of ten
amateur golfers having head speeds of 35 to 40 m/s and using W#1
clubs. Ratings were based on the following criteria. [0089] Good:
At least 7 of the 10 golfers thought the ball had a good feel.
[0090] Fair: Five or six of the 10 golfers thought the ball had a
good feel. [0091] Poor: Four or fewer of the 10 golfers thought the
ball had a good feel.
Scuff Resistance
[0092] A non-plated X-WEDGE 03 (loft, 52.degree.) manufactured by
Bridgestone Sports Co., Ltd. was set in a swing robot, and the ball
was hit at a head speed of 33 m/s with the club face open about
30.degree. from square. The surface state of the ball was then
visually examined by three golfers having handicaps of 10 or less,
and rated according to the following criteria. The average of the
ratings obtained for each example is shown in the table. [0093] 5:
Surface of ball is either completely unchanged or bears a slight
imprint from club face. [0094] 4: Surface of ball bears a clear
imprint from club face, but is not frayed. [0095] 3: Surface is
conspicuously frayed and scuffed. [0096] 2: Surface is frayed and
cracked. [0097] 1: Some dimples have been obliterated.
[0098] It is apparent from the results in Table 1 that the golf
balls obtained in the examples of the invention had excellent
rebound resilience, scuff resistance and feel on impact. By
contrast, the balls obtained in the comparative examples had a poor
feel and showed no improvement in scuff resistance.
* * * * *