U.S. patent application number 13/728404 was filed with the patent office on 2014-07-03 for golf ball.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. The applicant listed for this patent is BRIDGESTONE SPORTS CO., LTD.. Invention is credited to Atsushi NANBA, Takanori TAGO.
Application Number | 20140187357 13/728404 |
Document ID | / |
Family ID | 51017805 |
Filed Date | 2014-07-03 |
United States Patent
Application |
20140187357 |
Kind Code |
A1 |
TAGO; Takanori ; et
al. |
July 3, 2014 |
GOLF BALL
Abstract
The present invention, by forming the outermost layer of a golf
ball cover from a specific resin composition that includes a
thermoplastic resin and a color masterbatch having mutually similar
specific gravities, provides a golf ball which is imparted with an
excellent durability of markings thereon, a uniform and evenly
colored appearance, and an excellent manufacturability.
Inventors: |
TAGO; Takanori;
(Chichibushi, JP) ; NANBA; Atsushi; (Chichibushi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BRIDGESTONE SPORTS CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Family ID: |
51017805 |
Appl. No.: |
13/728404 |
Filed: |
December 27, 2012 |
Current U.S.
Class: |
473/385 |
Current CPC
Class: |
A63B 45/00 20130101;
A63B 37/0087 20130101; A63B 37/0036 20130101; A63B 37/0076
20130101; A63B 37/0074 20130101; A63B 37/008 20130101; A63B 37/0022
20130101; C08L 23/0876 20130101; C08L 23/0876 20130101; C08L 23/08
20130101 |
Class at
Publication: |
473/385 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Claims
1. A golf ball comprising a core and a cover of at least one layer
encasing the core, wherein an outermost layer of the cover is
formed of a resin composition comprising: (A) a thermoplastic
resin, and (B) a color masterbatch, which color masterbatch (B)
includes (b-1) a thermoplastic resin, (b-2) a colorant, (b-3)
titanium oxide, (b-4) a fatty acid metal salt, and (b-5) a
dispersant, component (b-4) being included in an amount of from 0.3
to 1.4 parts by weight per 100 parts by weight of component (A) and
component (b-1) combined, the ratio (B)/(A) of the specific gravity
of component (A) to the specific gravity of component (B) being
from 0.8 to 1.2, and component (A) and component (b-1) having
weight-average molecular weights (Mw) of at least 100,000.
2. The golf ball of claim 1, wherein the thermoplastic resin (A) is
one or more selected from the group consisting of: (a-1) an
olefin-unsaturated carboxylic acid copolymer, (a-2) a metal ion
neutralization product of an olefin-unsaturated carboxylic acid
copolymer, (a-3) an olefin-unsaturated carboxylic acid-unsaturated
carboxylic acid ester terpolymer, and (a-4) a metal ion
neutralization product of an olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester terpolymer.
3. The golf ball of claim 2, wherein at least 30 wt % of the
unsaturated carboxylic acid included in (a-2) the metal ion
neutralization product of an olefin-unsaturated carboxylic acid
copolymer and/or (a-4) the metal ion neutralization product of an
olefin-unsaturated carboxylic acid-unsaturated carboxylic acid
ester terpolymer is neutralized with metal ions.
4. The golf ball of claim 2, wherein (a-2) the metal ion
neutralization product of an olefin-unsaturated carboxylic acid
copolymer and/or (a-4) the metal ion neutralization product of an
olefin-unsaturated carboxylic acid-unsaturated carboxylic acid
ester terpolymer include as the metal ions one or more selected
from the group consisting of Li.sup.+, Na.sup.+, Mg.sup.++,
Ca.sup.++ and Zn.sup.++.
5. The golf ball of claim 2, wherein component (A) further includes
(a-5) one or more selected from the group consisting of
polyethylene, thermoplastic polyurethane and rubbery elastomer.
6. The golf ball of claim 1, wherein the thermoplastic resin
serving as component (b-1) is one or more selected from the group
consisting of: (b-1-1) an olefin-unsaturated carboxylic acid
copolymer, and (b-1-2) an olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester terpolymer.
7. The golf ball of claim 1, wherein the thermoplastic resin
serving as component (b-1) has a melt flow rate (MFR) of from 5 to
60 g/10 min.
8. The golf ball of claim 1, wherein the colorant (b-2) is one or
more selected from the group consisting of red, blue, yellow,
orange, green, violet and black colorants.
9. The golf ball of claim 1, wherein the fatty acid metal salt
(b-4) is a metal salt of a fatty acid having from 16 to 30
carbons.
10. The golf ball of claim 1, wherein the fatty acid component of
the fatty acid metal salt (b-4) is one or more selected from the
group consisting of stearic acid, oleic acid, behenic acid and
montanic acid.
11. The golf ball of claim 1, wherein the metal ion of the fatty
acid metal salt (b-4) is one or more selected from the group
consisting of Li.sup.+, Na.sup.+, Mg.sup.++, Ca.sup.++ and
Zn.sup.++.
12. The golf ball of claim 1, wherein component (B) is included in
an amount of from 3 to 25 parts by weight per 100 parts by weight
of component (A).
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a golf ball which has an
excellent durability of markings thereon, a uniform and evenly
colored appearance, and an excellent manufacturability.
[0002] Lately, not all golf balls have been white; balls in a
variety of colors are being manufactured and marketed in response
to the preferences of golfers. Such golf balls are generally
colored by including a colorant such as a pigment or dye in the
material used to form the outermost layer that serves as the ball
cover. The cover is typically formed by feeding a base resin and
various additives, colorant and the like in specific compounding
ratios into an injection molding machine, thoroughly mixing these
ingredients together within the molding machine, and injecting the
resulting mixture into a given mold. However, if the resin, the
various additives and the colorant have different specific
gravities, they do not readily mix uniformly at this time within
the injection molding machine, as a result of which color
unevenness sometimes arises on the molded cover. The solution taken
in such cases is to first prepare a masterbatch by mixing the
colorant into the base resin. However, further improvement is
required to better stabilize the quality.
[0003] Along with stabilizing the quality, it is also important to
lower production costs for the ball. Accordingly, there exists a
desire to find the production conditions that minimize trouble
during ball manufacture and thus enable stable production to be
carried out. In addition, the manufactured ball must also have an
excellent durability of markings thereon. Hence, it is desired that
markings on the ball not rub off during play and that the ball
maintain a good appearance.
[0004] Prior art relating to this invention has been disclosed in,
for example, JP-A 2012-105725, JP-A 2012-081111 and JP-A
2012-081110.
SUMMARY OF THE INVENTION
[0005] It is therefore an object of the invention to provide a golf
ball which has an excellent durability of markings thereon, a
uniform and evenly colored appearance, and an excellent
manufacturability.
[0006] As a result of intensive investigations, the inventors have
discovered that by optimizing the specific gravities of the base
resin and the masterbatch included in the material used to form the
outermost layer of a golf ball cover, and by also optimizing the
amount of fatty acid metal salt included within this material, a
golf ball having an excellent durability of markings thereon, a
uniform and evenly colored appearance and an excellent
manufacturability can be obtained.
[0007] Accordingly, the invention provides the following golf
ball.
[1] A golf ball comprising a core and a cover of at least one layer
encasing the core, wherein an outermost layer of the cover is
formed of a resin composition comprising:
[0008] (A) a thermoplastic resin, and
[0009] (B) a color masterbatch,
which color masterbatch (B) includes [0010] (b-1) a thermoplastic
resin, [0011] (b-2) a colorant, [0012] (b-3) titanium oxide, [0013]
(b-4) a fatty acid metal salt, and [0014] (b-5) a dispersant,
component (b-4) being included in an amount of from 0.3 to 1.4
parts by weight per 100 parts by weight of component (A) and
component (b-1) combined, the ratio (B)/(A) of the specific gravity
of component (A) to the specific gravity of component (B) being
from 0.8 to 1.2, and component (A) and component (b-1) having
weight-average molecular weights (Mw) of at least 100,000. [2] The
golf ball of [1], wherein the thermoplastic resin (A) is one or
more selected from the group consisting of: [0015] (a-1) an
olefin-unsaturated carboxylic acid copolymer, [0016] (a-2) a metal
ion neutralization product of an olefin-unsaturated carboxylic acid
copolymer, [0017] (a-3) an olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester terpolymer, and [0018] (a-4)
a metal ion neutralization product of an olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester terpolymer. [3]
The golf ball of [2], wherein at least 30 wt % of the unsaturated
carboxylic acid included in (a-2) the metal ion neutralization
product of an olefin-unsaturated carboxylic acid copolymer and/or
(a-4) the metal ion neutralization product of an olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester terpolymer is
neutralized with metal ions. [4] The golf ball of [2], wherein
(a-2) the metal ion neutralization product of an olefin-unsaturated
carboxylic acid copolymer and/or (a-4) the metal ion neutralization
product of an olefin-unsaturated carboxylic acid-unsaturated
carboxylic acid ester terpolymer include as the metal ions one or
more selected from the group consisting of Li.sup.+, Na.sup.+,
Mg.sup.++, Ca.sup.++ and Zn.sup.++. [5] The golf ball of [2],
wherein component (A) further includes (a-5) one or more selected
from the group consisting of polyethylene, thermoplastic
polyurethane and rubbery elastomer. [6] The golf ball of [1],
wherein the thermoplastic resin serving as component (b-1) is one
or more selected from the group consisting of: [0019] (b-1-1) an
olefin-unsaturated carboxylic acid copolymer, and [0020] (b-1-2) an
olefin-unsaturated carboxylic acid-unsaturated carboxylic acid
ester terpolymer. [7] The golf ball of [1], wherein the
thermoplastic resin serving as component (b-1) has a melt flow rate
(MFR) of from 5 to 60 g/10 min. [8] The golf ball of [1], wherein
the colorant (b-2) is one or more selected from the group
consisting of red, blue, yellow, orange, green, violet and black
colorants. [9] The golf ball of [1], wherein the fatty acid metal
salt (b-4) is a metal salt of a fatty acid having from 16 to 30
carbons. [10] The golf ball of [1], wherein the fatty acid
component of the fatty acid metal salt (b-4) is one or more
selected from the group consisting of stearic acid, oleic acid,
behenic acid and montanic acid. [11] The golf ball of [1], wherein
the metal ion of the fatty acid metal salt (b-4) is one or more
selected from the group consisting of Li.sup.+, Na.sup.+,
Mg.sup.++, Ca.sup.++ and Zn.sup.++. [12] The golf ball of [1],
wherein component (B) is included in an amount of from 3 to 25
parts by weight per 100 parts by weight of component (A).
BRIEF DESCRIPTION OF THE DIAGRAMS
[0021] FIG. 1 is a schematic cross-sectional diagram showing an
example of the construction of a golf ball according to the
invention.
[0022] FIG. 2 is a top view showing the markings that were placed
on the golf balls fabricated in the examples of the invention and
the comparative examples.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The invention is described more fully below.
[0024] The golf ball of the invention has a cover with an outermost
layer that is formed using a specific resin composition which
includes a thermoplastic resin and a color masterbatch having
mutually similar specific gravities. The ball construction, so long
as it includes a core and a cover of at least one layer, may be
suitably set within a range that satisfies the objects of the
invention. FIG. 1 shows an exemplary construction of the golf ball
of the invention. The golf ball G shown in FIG. 1 is a two-piece
solid golf ball having a core 1 and a cover 2 that encases the
core. The cover 2 has a surface on which, typically, a plurality of
dimples D are formed. In the diagram, the core 1 and the cover 2
are each formed as single layers, although either or both may be
composed of a plurality of layers.
[0025] The golf ball of the invention is described in detail below
while referring to FIG. 1.
[0026] First, the material used to form the core 1 is described.
The core 1 is obtained by vulcanizing a rubber composition made up
primarily of a rubber material. Specifically, use may be made of a
rubber composition containing, for example, a base rubber, a
crosslinking initiator and a co-crosslinking agent.
[0027] The base rubber of the rubber composition is not subject to
any particular limitation, although the use of polybutadiene is
preferred. Preferred use may be made of cis-1,4 polybutadiene
having a cis structure content of at least 40%. If so desired, in
the base rubber, other rubbers such as natural rubber, polyisoprene
rubber or styrene-butadiene rubber may be suitably compounded with
the above polybutadiene.
[0028] Preferred use may be made of an organic peroxide as the
crosslinking initiator in the present invention. Illustrative
examples of suitable organic peroxides include
1,1-di(t-butylperoxy)cyclohexane,
1,1-bis-t-butylperoxy-3,3,5-trimethylcyclohexane, dicumyl peroxide,
di(t-butylperoxy)-meta-diisopropylbenzene and
2,5-dimethyl-2,5-di-t-butylperoxyhexane. A commercial product may
be used as the organic peroxide. Examples of such products include
Perhexa C-40, Perhexa 3M-40 and Percumyl D (available from NOF
Corporation) and Trigonox 29-40 (available from Kayaku Akzo
Corporation). These crosslinking initiators are compounded in an
amount which, although not subject to any particular limitation, is
preferably at least 0.1 part by weight, and more preferably at
least 0.3 part by weight, per 100 parts by weight of the base
rubber. The upper limit is preferably not more than 5 parts by
weight, and more preferably not more than 2 parts by weight.
[0029] The co-crosslinking agent used in the invention may be, for
example, a metal salt of an unsaturated fatty acid such as
methacrylic acid or acrylic acid (e.g., zinc salts, magnesium
salts, calcium salts), or an ester compound such as
trimethylolpropane trimethacrylate. To obtain a high rebound in
particular, preferred use may be made of zinc acrylate. The amount
of such co-crosslinking agents included per 100 parts by weight of
the base rubber, although not subject to any particular limitation,
may be set to at least 10 parts by weight, and preferably at least
15 parts by weight, but not more than 50 parts by weight, and
preferably not more than 40 parts by weight.
[0030] In addition, various additives may be optionally included in
the above composition, examples of such additives being sulfur,
antioxidant, zinc oxide, barium sulfate, the zinc salt of
pentachlorothiophenol, and zinc stearate. No particular limitation
is imposed on the amounts in which these additives are
included.
[0031] The core diameter, although not particularly limited, may be
set to preferably at least 32.0 mm, and more preferably at least
33.0 mm. The upper limit is preferably not more than 42.0 mm, and
more preferably not more than 41.0 mm. The core coloration also is
not subject to any particular limitation.
[0032] Next, the material used to form the cover 2 is
described.
[0033] In this invention, the cover-forming material is a resin
composition which includes:
[0034] (A) a thermoplastic resin, and
[0035] (B) a color masterbatch.
[0036] The thermoplastic resin serving as component (A) is not
subject to any particular limitation, although preferred use can be
made of one or more selected from the group consisting of: [0037]
(a-1) an olefin-unsaturated carboxylic acid copolymer, [0038] (a-2)
a metal ion neutralization product of an olefin-unsaturated
carboxylic acid copolymer, [0039] (a-3) an olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester terpolymer, and
[0040] (a-4) a metal ion neutralization product of an
olefin-unsaturated carboxylic acid-unsaturated carboxylic acid
ester terpolymer. In this invention, (a-5) one or more selected
from the group consisting of polyethylene, thermoplastic
polyurethane and rubbery elastomer may be additionally
included.
[0041] In the olefin unsaturated carboxylic acid copolymer
(component a-1) of above component (A), the number of carbons on
the olefin is typically at least 2 and not more than 8, and is
preferably not more than 6. Specific examples include ethylene,
propylene, butene, pentene, hexene, heptene and octene. Ethylene is
especially preferred. Examples of unsaturated carboxylic acids
include acrylic acid, methacrylic acid, maleic acid (anhydride) and
fumaric acid. Acrylic acid and methacrylic acid are especially
preferred.
[0042] Component (a-2) is obtained by neutralizing the unsaturated
carboxylic acid included in above component (a-1) with a metal ion.
The metal ion which neutralizes the unsaturated carboxylic acid is
preferably one or more metal ion selected from the group consisting
of Li.sup.+, Na.sup.+, K.sup.+, Mg.sup.++, Ca.sup.++, Zn.sup.++,
Cu.sup.++, Ba.sup.++, Pb.sup.++ and Al.sup.+++. Neutralization with
one or more metal ion selected from the group consisting of
Li.sup.+, Na.sup.+, Mg.sup.++, Ca.sup.++ and Zn.sup.++ is
especially preferred.
[0043] Although not subject to any particular limitation, it is
recommended that preferably at least 30 wt %, more preferably at
least 40 wt %, and even more preferably at least 50 wt %, of the
unsaturated carboxylic acid included in the copolymer of component
(a-2) be neutralized with metal ions.
[0044] In the olefin unsaturated carboxylic acid-unsaturated
carboxylic acid ester terpolymer serving as component (a-3), the
olefin and the unsaturated carboxylic acid may be the same as in
component (a-1). As the unsaturated carboxylic acid ester,
preferred use can be made of, for example, lower alkyl esters of
the above-described unsaturated carboxylic acids. Illustrative
examples include methyl methacrylate, ethyl methacrylate, propyl
methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate,
propyl acrylate and butyl acrylate. The use of butyl acrylate
(n-butyl acrylate, isobutyl acrylate) is especially preferred.
[0045] Component (a-4) is obtained by neutralizing the unsaturated
carboxylic acid included in above component (a-3) with a metal ion.
The metal ion which neutralizes the unsaturated carboxylic acid is
exemplified by the same ions as in component (a-2). Preferred
examples include metal ions selected from the group consisting of
Li.sup.+, Na.sup.+, K.sup.+, Mg.sup.++, Zn.sup.++, Cu.sup.++,
Ba.sup.++, Pb.sup.++ and Al.sup.+++. Neutralization with a metal
ion selected from the group consisting of Li.sup.+, Na.sup.+,
Mg.sup.++, Ca.sup.++ and Zn.sup.++ is especially preferred.
[0046] Although not subject to any particular limitation, as in
component (a-2), it is recommended that preferably at least 30 wt
%, more preferably at least 40 wt %, and even more preferably at
least 50 wt %, of the unsaturated carboxylic acid included in the
terpolymer of component (a-4) be neutralized with metal ions.
[0047] Component (a-5) is one or more component selected from the
group consisting of polyethylene, thermoplastic polyurethane and
rubbery elastomer. Known substances may be used as any of these.
Although not subject to any particular limitation, especially
preferred examples of rubbery elastomers include styrene-butadiene
copolymers (SBR), styrene-butadiene-styrene copolymers (SBS),
hydrogenated styrene-butadiene copolymers (H-SBR),
styrene-ethylene/butene-styrene copolymers (SEBS), hydrogenated
styrene-isoprene-styrene copolymers (SEPS),
styrene-isoprene/butadiene-styrene copolymers (SIBS), hydrogenated
styrene-isoprene/butadiene-styrene copolymers (SEEPS),
styrene-isoprene-styrene copolymers (SIS), hydrogenated
styrene-ethylene/butylene-olefin crystalline block copolymers
(SEBC) and hydrogenated olefin crystalline
block-ethylene/butylene-olefin crystalline block copolymers
(CEBC).
[0048] The weight-average molecular weight (Mw) of above component
(A) may be set to at least 100,000, and preferably at least
110,000. The upper limit may be set to preferably not more than
200,000, and more preferably not more than 190,000. If the
weight-average molecular weight (Mw) is too small, the flow
properties of the material may be too high, which often leads to a
loss of homogeneity in the material at the time of injection
molding. Moreover, obtaining a resilience and durability to impact
sufficient for a golf ball is difficult. On the other hand, if the
weight-average molecular weight (Mw) is too large, the flow
properties may become too low, which may make it impossible to
obtain a good moldability.
[0049] The above copolymer has a weight-average molecular weight
(Mw) to number-average molecular weight (Mn) ratio which, although
not particularly limited, may be set to preferably at least 2.0,
and more preferably at least 2.5. The upper limit may be set to
preferably not more than 10.0, and more preferably not more than
9.5.
[0050] Here, the weight-average molecular weight (Mw) and
number-average molecular weight (Mn) are values calculated relative
to polystyrene in gel permeation chromatography (GPC). A word of
explanation is needed here concerning GPC molecular weight
measurement. It is not possible to directly take GPC measurements
for copolymers and terpolymers because these molecules are adsorbed
to the GPC column owing to unsaturated carboxylic acid groups
within the molecules. Instead, the unsaturated carboxylic acid
groups are generally converted to esters, following which GPC
measurement is carried out and the polystyrene-equivalent average
molecular weights Mw and Mn are calculated.
[0051] A commercial product may be used as component (A).
Illustrative examples include the following.
[0052] Illustrative examples of component (a-1) include
ethylene-methacrylic acid copolymers such as Nucrel N1035, Nucrel
N1525, Nucrel N1560, Nucrel N1050H, Nucrel N1110H and Nucrel N2050H
(all available from DuPont-Mitsui Polychemicals Co., Ltd.), and
ethylene-acrylic acid copolymers such as Primacor 59801 (Dow
Chemical).
[0053] Illustrative examples of component (a-2) include Himilan
1601 (Na), Himilan 1555 (Na), Himilan 1557 (Zn), Himilan 1605 (Na),
Himilan 1706 (Zn), Himilan 1707 (Na), Himilan AM7311 (Mg) and
Himilan AM7329 (Zn) (all available from DuPont-Mitsui Polychemicals
Co., Ltd.). Additional examples include Surlyn 8945 (Na), Surlyn
9945 (Zn), Surlyn 8150 (Na), Surlyn 9120 (Zn), Surlyn 9150 (Zn),
Surlyn 6910 (Mg), Surlyn 6120 (Mg), Surlyn 7930 (Li) and Surlyn
7940 (Li) (all available from E.I. DuPont de Nemours & Co.);
and Iotek 8000 (Na), Iotek 8030 (Na), Iotek 7010 (Zn) and Iotek
7030 (Zn) (all available from ExxonMobil Chemical).
[0054] Illustrative examples of component (a-3) include Nucrel
AN4318 and Nucrel AN4319 (DuPont-Mitsui Polychemicals Co., Ltd.),
Nucrel AE (E.I. DuPont de Nemours & Co.), and Primacor AT310
and Primacor AT320 (Dow Chemical).
[0055] Illustrative examples of component (a-4) include Himilan
AM7327 (Zn), Himilan 1855 (Zn), Himilan 1856 (Na) and Himilan
AM7331 (Na) (DuPont-Mitsui Polychemicals Co., Ltd.). Additional
examples include terpolymeric ionomer resins such as Surlyn 6320
(Mg), Surlyn 8320 (Na) and Surlyn 9320 (Zn) (E. I. DuPont de
Nemours & Co.), and Iotek 7510 (Zn) and Iotek 7520 (Zn)
(ExxonMobil Chemical).
[0056] The symbols Na, Zn and Mg appearing in parentheses after the
trade names indicate the type of neutralizing metal ion.
[0057] Illustrative examples of component (a-5) include the
following commercial products.
[0058] First, exemplary polyethylenes include the high-pressure
low-density polyethylenes UBE Polyethylene R300, UBE Polyethylene
F120N and UBE Polyethylene J1019 (all available from Ube-Maruzen
Polyethylene). Exemplary thermoplastic polyurethanes include Pandex
T8180, Pandex T8195, Pandex T8290, Pandex T8295 and Pandex T8260
(all available from DIC Bayer Polymer, Ltd.), and Resamine 2593 and
Resamine 2597 (Dainichiseika Color & Chemicals Mfg. Co., Ltd.).
Exemplary rubbery elastomers include the hydrogenated polymers
Dynaron 6100P and Dynaron 6200P (JSR Corporation).
[0059] The specific gravity of component (A), although not
particularly limited, may be set to preferably at least 0.8, and
more preferably at least 0.85. The upper limit may be set to
preferably not more than 1.2, and more preferably not more than
1.15.
[0060] The melt flow rate (MFR) of component (A) is not subject to
any particular limitation. However, from the standpoint of
providing good flow properties and molding processability during
injection molding, the MFR, as measured in accordance with JIS
K-7210 at a test temperature of 190.degree. C. and a test load of
21.18 N (2.16 kgf), is set to preferably at least 0.1 g/10 min,
more preferably at least 0.5 g/10 min, and even more preferably at
least 0.8 g/10 min. It is recommended that the upper limit be set
to preferably not more than 30 g/10 min, more preferably not more
than 25 g/10 min, and even more preferably not more than 20 g/10
min. In cases where the MFR of component (A) is too large, the flow
properties of the material may become too high, which often leads
to a loss in the homogeneity of the material during injection
molding. Moreover, obtaining a resilience and durability to impact
sufficient for a golf ball may become difficult. On the other hand,
if the MFR of component (A) is too small, the flow properties may
become too low, as a result of which a good moldability may not be
attainable.
[0061] The color masterbatch serving as component (B) is obtained
by mixing a colorant with a known resin and additives. In this
invention, advantageous use may be made of a resin composition
containing the following components (b-1) to (b-5): [0062] (b-1) a
thermoplastic resin, [0063] (b-2) a colorant, [0064] (b-3) titanium
oxide, [0065] (b-4) a fatty acid metal salt, and [0066] (b-5) a
dispersant.
[0067] A known resin may be used as the thermoplastic resin serving
as component (b-1). Although not subject to any particular
limitation, preferred use may be made of one or more selected from
the group consisting of: [0068] (b-1-1) an olefin-unsaturated
carboxylic acid copolymer, and [0069] (b-1-2) an olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester terpolymer.
[0070] The olefin-unsaturated carboxylic acid copolymer serving as
component (b-1-1) is exemplified by the same copolymers as
component (a-1) above. In this case, the number of carbons on the
olefin included in component (b-1-1) is typically at least 2 and
not more than 8, and is preferably not more than 6. Specific
examples of such olefins include ethylene, propylene, butene,
pentene, hexene, heptene and octene. Ethylene is especially
preferred. Examples of unsaturated carboxylic acids include acrylic
acid, methacrylic acid, maleic acid (anhydride) and fumaric acid.
Acrylic acid and methacrylic acid are especially preferred.
[0071] The olefin-unsaturated carboxylic acid-unsaturated
carboxylic acid ester terpolymer serving as component (b-1-2) is
exemplified by the same copolymers as component (b-1-1) above. As
the unsaturated carboxylic acid ester, preferred use can be made
of, for example, lower alkyl esters of the above-mentioned
unsaturated carboxylic acids. Illustrative examples include methyl
methacrylate, ethyl methacrylate, propyl methacrylate, butyl
methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate and
butyl acrylate. The use of butyl acrylate (n-butyl acrylate,
isobutyl acrylate) is especially preferred.
[0072] The weight-average molecular weight (Mw) of above component
(b-1) may be set to at least 100,000, and preferably at least
110,000. The upper limit may be set to preferably not more than
200,000, and more preferably not more than 190,000. If the
weight-average molecular weight (Mw) is too small, the flow
properties of the material may be too high, which often leads to a
loss of homogeneity in the material at the time of injection
molding and to color unevenness. Moreover, obtaining a resilience
and durability to impact sufficient for a golf ball is difficult.
On the other hand, if the weight-average molecular weight (Mw) is
too large, the flow properties may become too low, making it
impossible to obtain a good moldability, in addition to which the
dispersibility of the colorant may worsen, which may give rise to
color unevenness.
[0073] The above copolymer has a weight-average molecular weight
(Mw) to number-average molecular weight (Mn) ratio which, although
not particularly limited, is set to preferably at least 2.0, and
more preferably at least 2.5. The upper limit is preferably set to
not more than 10.0, and more preferably not more than 9.5.
[0074] A commercial product may be used as component (b-1).
Illustrative examples include the following.
[0075] Examples of component (b-1-1) include ethylene-methacrylic
acid copolymers such as Nucrel N1035, Nucrel N1525, Nucrel N1560,
Nucrel N1050H, Nucrel N1110H and Nucrel N2050H (all available from
DuPont-Mitsui Polychemicals Co., Ltd.), and ethylene-acrylic acid
copolymers such as Primacor 59801 (Dow Chemical).
[0076] Examples of component (b-1-2) include Nucrel AN4318 and
Nucrel AN4319 (both available from DuPont-Mitsui Polychemicals Co.,
Ltd.), Nucrel AE (E.I. DuPont de Nemours & Co.), and Primacor
AT310 and Primacor AT320 (Dow Chemical).
[0077] The content of component (b-1) in component (B), although
not particularly limited, is preferably set to at least 10 wt %,
and is more preferably at least 15 wt %, and even more preferably
at least 20 wt %. The upper limit is preferably set to not more
than 99.9 wt %, and is more preferably not more than 99.7 wt %, and
even more preferably not more than 99.5 wt %. If the content of
component (b-1) is too small, it may not be possible to obtain
pellets of a suitable shape during preparation of the color
masterbatch, as a result of which charging of the color masterbatch
into the molding machine during molding of the cover may be
difficult. On the other hand, if the content of component (b-1) is
too large, the proportion of component (b-1) relative to the
contents of components (A) and (B) increases, which may make it
difficult to obtain a resilience sufficient for a golf ball.
[0078] The melt flow rate (MFR) of component (b-1) is not subject
to any particular limitation. However, from the standpoint of
providing good flow properties and molding processability during
injection molding, the MFR, as measured in accordance with JIS
K-7210 at a test temperature of 190.degree. C. and a test load of
21.18 N (2.16 kgf), may be set to preferably at least 5 g/10 min,
more preferably at least 7 g/10 min, and even more preferably at
least 10 g/10 min. It is recommended that the upper limit be set to
preferably not more than 60 g/10 min, more preferably not more than
55 g/10 min, and even more preferably not more than 50 g/10 min. In
cases where the MFR of component (b-1) is too large (the flow
properties are too high), this often leads to a loss of homogeneity
in the material during injection molding, and color unevenness.
Moreover, obtaining a resilience and durability to impact
sufficient for a golf ball may be difficult. In cases where the MFR
of component (b-1) is too small (the flow properties are too low),
it may not be possible to obtain a good moldability, in addition to
which the dispersibility of the colorant may worsen and color
unevenness may arise.
[0079] The colorant serving as component (b-2) is included for the
purpose of adjusting the color of the ball. In the practice of the
invention, a known pigment or dye may be used. From the standpoint
of resistance to discoloration, it may be preferable to use a
pigment. The colorant is suitably selected from the group
consisting of red colorants, blue colorants, yellow colorants,
orange colorants, green colorants, violet colorants and black
colorants. Exemplary red colorants include those based on
quinacridones, perylenes and anthraquinones; exemplary blue
colorants include those based on phthalocyanines and ultramarine;
exemplary yellow colorants include complex oxide colorants, polyazo
colorants and heterocyclic colorants; exemplary violet colorants
include ultramarine violet; and black colorants include carbon
black. By including these, it is possible to express a color having
a sense of elegance. These color pigments or dyes may be used
singly, or two or more may be used together; the combinations or
included amounts of the color pigments or dyes may be suitably
selected according to the ball specifications and other
considerations. Commercial products may be used as the color
pigment or dye. Specific examples of such commercial products
include those available under the trade names CHROMOFINE (Dainichi
Seika Color & Chemicals Mfg. Co., Ltd.), TIPAQUE YELLOW
(Ishihara Sangyo Kaisha, Ltd.) and TOKABLACK (Tokai Carbon Co.,
Ltd.). The content of component (b-2) in component (B), although
not particularly limited, is preferably set to at least 0.1 wt %,
more preferably at least 0.2 wt %, and even more preferably at
least 0.3 wt %. The upper limit is preferably set to not more than
90 wt %, more preferably not more than 80 wt %, and even more
preferably not more than 70 wt %. If the content of component (b-2)
is too low, a sufficient coloration may not be obtained. On the
other hand, if the content of component (b-2) is too high, it may
not be possible to obtain pellets of a suitable shape, as a result
of which charging of the color masterbatch into the molding machine
during molding of the cover may be difficult. Moreover, obtaining a
resilience and durability to impact sufficient for a golf ball may
be difficult.
[0080] The titanium oxide used as component (b-3) may be a known
titanium oxide. For example, preferred use may be made of the
products commercially available under the trade name TIPAQUE (from
Ishihara Sangyo Kaisha). The content of component (b-3) in
component (B), although not particularly limited, is set to
preferably at least 0.01 wt %, more preferably at least 0.5 wt %,
and even more preferably at least 0.1 wt %. The upper limit is
preferably set to not more than 30 wt %, and is more preferably not
more than 20 wt %, and even more preferably not more than 10 wt
%.
[0081] The fatty acid metal salt serving as component (b-4) is not
particularly limited, although preferred use may be made of a metal
salt of a fatty acid having from 16 to 30 carbons. The metal ion
included in the fatty acid metal salt may be one or more selected
from the group consisting of Li.sup.+, Na.sup.+, Mg.sup.++,
Ca.sup.++ and Zn.sup.++. Illustrative examples include the sodium
salts, zinc salts, magnesium salts, calcium salts and lithium salts
of stearic acid, oleic acid, behenic acid and montanic acid. In the
practice of the invention, the use of magnesium stearate, calcium
stearate, zinc stearate, magnesium behenate or magnesium montanate
is especially preferred. The content of component (b-4) in
component (B), although not particularly limited, may be set to
preferably at least 1.8 wt %, more preferably at least 2.4 wt %,
and even more preferably at least 3.0 wt %. The upper limit is
preferably set to not more than 29.0 wt %, more preferably not more
than 27.0 wt %, and even more preferably not more than 25.0 wt
%.
[0082] The content of above component (b-4) in the overall
cover-forming material must be set to at least 0.3 part by weight
per 100 parts by weight of above component (A) and component (b-1)
combined; it is recommended that this content by set to preferably
at least 0.4 part by weight, and more preferably at least 0.5 part
by weight. The upper limit must be set to not more than 1.4 parts
by weight; it is recommended that this upper limit be set to not
more than 1.3 parts by weight, and more preferably not more than
1.2 parts by weight. If the content of component (b-4) is too low,
sufficient releasability from the mold may not be obtained. On the
other hand, if the content of component (b-4) is too high, the
durability of markings on the golf ball cover may decrease.
[0083] A known dispersant may be used as the dispersant serving as
component (b-5). Although not subject to any particular limitation,
preferred use can be made of, for example, a polyethylene wax or a
cationic group-containing acrylic polymer. The content of above
component (b-5) in component (B), although not particularly
limited, is preferably set to at least 0.01 wt %, more preferably
at least 0.5 wt %, and even more preferably at least 0.1 wt %. The
upper limit is preferably set to not more than 10.0 wt %, more
preferably not more than 9.0 wt %, and even more preferably not
more than 8.0 wt %. If the content of component (b-5) is too low,
the dispersibility of the colorant and titanium oxide in the
masterbatch may worsen. On the other hand, if the content of
component (b-5) is too high, it may not be possible to obtain
pellets of a suitable shape during preparation of the color
masterbatch, as a result of which charging of the color masterbatch
into the molding machine during molding of the cover may be
difficult. Moreover, obtaining a resilience and durability to
impact sufficient for a golf ball may be difficult.
[0084] The specific gravity of component (B), although not
particularly limited, may be set to preferably at least 0.8, and
more preferably at least 0.85. The upper limit may be set to
preferably not more than 1.2, and more preferably not more than
1.15.
[0085] The ratio (B)/(A) of the specific gravity of component (A)
to the specific gravity of component (B) must be at least 0.8, and
may be set to preferably at least 0.85. The upper limit must be not
more than 1.2, and may be set to preferably not more than 1.15.
When the specific gravity ratio falls outside of the above range,
the material may not mix uniformly and color unevenness may arise
in the cover after molding.
[0086] The amount of component (B) included in the cover-forming
material, although not particularly limited, is preferably at least
3 parts by weight, more preferably at least 4 parts by weight, and
even more preferably at least 5 parts by weight, per 100 parts by
weight of component (A). The upper limit is preferably set to not
more than 25 parts by weight, and is more preferably not more than
23 parts by weight, and even more preferably not more than 20 parts
by weight. If the amount of component (B) included is too low, the
material may not mix uniformly and color unevenness may arise in
the cover after molding. On the other hand, if the amount of
component (B) included is too high, the proportion of component
(b-1) relative to the content of components (A) and (B) becomes
high, which may make it difficult to obtain a resilience sufficient
for a golf ball.
[0087] The color masterbatch serving as component (B) may be
prepared by a known method. For example, the color masterbatch may
be obtained by mixture using a mixing apparatus selected from among
twin-screw/single-screw extruders (including kneader-extruders)
equipped with a pressurizing kneader and a force feeder, tandem
extruders, and twin-screw extruders. These extruders need not be of
a special design; the use of an existing extruder will suffice.
[0088] In addition, various types of additives, such as ultraviolet
absorbers, antioxidants, metal soaps and inorganic fillers other
than those mentioned above, may be suitably included in this
cover-forming material.
[0089] Preparation of the resin composition containing above
components (A) and (B) may be carried out using a known mixing
apparatus, such as a single-screw extruder or a twin-screw
extruder. In this invention, the use of a twin-screw extruder is
preferred. Alternatively, these extruders may be used in a tandem
arrangement, such as single-screw extruder/twin-screw extruder or
twin-screw extruder/twin-screw extruder. These extruders need not
be of a special design; the use of an existing extruder will
suffice. The method of molding the cover using the above resin
composition is not subject to any particular limitation. For
example, use may be made of an injection molding process or a
compression molding process. In cases where an injection molding
process is used, the process may be one in which a prefabricated
core is placed at a predetermined position in an injection mold,
following which the resin composition is introduced into the
mold.
[0090] Alternatively, in cases where a compression-molding process
is used, the process may be one in which a pair of half-cups are
fashioned beforehand by an injection-molding process or the like
from the above resin composition, following which the cups are
placed over the core, and heat and pressure are applied in a mold.
When molding is carried out under applied heat and pressure, the
molding conditions employed may be a temperature of from 120 to
170.degree. C. and a molding time of from 1 to 5 minutes.
[0091] The thickness per layer of the cover may be suitably set
without particular limitation according to such considerations as
the construction and materials of the golf ball to be produced,
although the thickness is set to preferably at least 0.1 mm, and
more preferably at least 0.2 mm. There is no particular upper
limit, although the thickness per cover layer may be set to
preferably not more than 4 mm, and more preferably not more than 3
mm.
[0092] In cases where a multi-piece solid golf ball having a cover
of two or more layers formed over a core is to be produced, known
resin materials may be used without particular limitation to form
the layer or layers of the cover other than the outermost layer
(i.e., intermediate layer or layers).
[0093] In the above golf ball, the shapes, number and arrangement
of the dimples formed on the surface may be suitably set according
to the ball specifications, and are not subject to any particular
limitations. For example, the dimple shapes may be suitably
selected from among not only circular shapes, but also non-circular
polygonal shapes, dewdrop shapes and oval shapes. The diameter of
the above dimples, although not particularly limited, is preferably
set in the range of 0.5 to 6 mm. In addition, the dimple depth,
although not particularly limited, is preferably set in the range
of 0.05 to 0.4 mm.
[0094] No particular limitation is imposed on the surface coverage
by the dimples on the surface of the ball. However, from the
standpoint of the aerodynamic properties, the surface coverage is
preferably set to at least 70%, more preferably at least 75%, and
even more preferably at least 80%.
[0095] The ball has a deflection when compressed under a final load
of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf)
which, although not particularly limited, may be set to preferably
at least 2.5 mm. The upper limit in the deflection may be set to
preferably not more than 7 mm.
[0096] The golf ball of the invention can be made to conform to the
Rules of Golf for competitive play. Specifically, the ball can be
formed to a diameter which is not less than 42.67 mm and to a
weight which is not more than 45.93 g.
[0097] As explained above, the present invention is able to provide
a golf ball which has an excellent durability such that markings on
the ball do not rub off during play, and which also has a uniform
and evenly colored appearance. Moreover, because this golf ball has
an excellent releasability from the mold and can be stably
produced, the ball also has an outstanding manufacturability.
EXAMPLES
[0098] Working Examples of the invention and Comparative Examples
are given below by way of illustration, and not by way of
limitation.
Examples 1 to 10, Comparative Examples 1 to 3
[0099] Cores having a diameter of 38.55 mm were produced by
preparing a rubber composition formulated as shown in Table 1,
using a kneader or a roll mill to masticate the composition, then
vulcanizing the composition at 155.degree. C. for 17 minutes.
TABLE-US-00001 TABLE 1 A B Formulation Polybutadiene rubber 100 100
(parts by weight) Zinc oxide 4 4 Barium sulfate 20.8 21 Titanium
oxide 2 Antioxidant 0.1 0.1 Zinc salt of pentachlorothiophenol 0.6
0.3 Zinc acrylate 25 23 Organic Peroxide 1 0.6 0.6 Organic Peroxide
2 0.6 0.6
[0100] Details on the ingredients shown in Table 1 are given below.
[0101] Polybutadiene rubber: Available as "BR01" from JSR
Corporation [0102] Zinc oxide: Available from Sakai Chemical Co.,
Ltd. [0103] Barium sulfate: Available as "Precipitated Barium
Sulfate 100" from Sakai Chemical Co., Ltd. [0104] Titanium oxide:
Available as "Tipaque R550" from Ishihara Sangyo Kaisha, Ltd.
[0105] Antioxidant: Available as "Nocrac NS-6" from Ouchi Shinko
Chemical Industry Co., Ltd. [0106] Zinc acrylate: Available from
Nihon Jyoryu Kogyo Co., Ltd. [0107] Organic Peroxide 1: Dicumyl
peroxide, available as "Percumyl D" from NOF Corporation [0108]
Organic Peroxide 2: 1,1-Bis(t-butylperoxy)cyclohexane diluted to
40% with an inorganic filler, available as "Perhexa C-40" from NOF
Corporation; half-life at 155.degree. C., about 50 seconds
[0109] Next, a color masterbatch or masterbatch formulated as shown
in Table 2 was prepared.
TABLE-US-00002 TABLE 2 No. 1 No. 2 No. 3 Formulation Nucrel N1035
92.03 74.80 (parts by weight) Nucrel N1050H 31.22 Titanium oxide
0.3 0.6 54 Polyethylene wax 0.23 5.93 0.51 Yellow dye 0.61 Yellow
pigment 12 Blue pigment 1.26 Magnesium stearate 6.83 6.67 13.01
[0110] Details on the ingredients shown in Table 2 are given below.
[0111] Nucrel N1035: An ethylene-methacrylic acid copolymer
available from DuPont-Mitsui [0112] Polychemicals Co., Ltd.; Mw,
168,000; MFR, 35 g/10 min [0113] Nucrel N1050: An
ethylene-methacrylic acid copolymer available from DuPont-Mitsui
Polychemicals Co., Ltd.; Mw, 61,000; MFR, 500 g/10 min [0114]
Titanium oxide: Available as "Tipaque R550" from Ishihara Sangyo
Kaisha, Ltd. [0115] Polyethylene wax: Available as "Sanwax 161P"
from Sanyo Chemical Industries, Ltd. [0116] Magnesium stearate:
Available as "Magnesium Stearate G" from NOF Corporation
[0117] A cover-forming material containing the color masterbatch or
masterbatch shown in Table 2 and the ingredients shown in Tables 3
to 5 was then injection-molded over the core obtained as described
above, thereby forming a cover having a thickness of 2.07 mm, and
the markings shown in FIG. 2 were thermal transfer printed onto the
surface thereof. Although not particularly described herein,
numerous dimples were formed in identical patterns on the surfaces
of the golf balls in each of the Working Examples of the invention
and the Comparative Examples.
TABLE-US-00003 TABLE 3 Example 1 2 3 4 5 6 Core Material A A A A A
A Diameter (mm) 38.55 38.55 38.55 38.55 38.55 38.55 Cover Thickness
(mm) 2.07 2.07 2.07 2.07 2.07 2.07 Color yellow yellow yellow
yellow yellow yellow Type of masterbatch dye dye dye dye dye dye
colorant Formulation (A) Himilan 1601 42.5 42.5 42.5 42.5 42.5 42.5
(pbw) Himilan 1557 42.5 42.5 42.5 42.5 42.5 42.5 Himilan 1605
Himilan 1706 Nucrel AN4319 15 15 15 15 15 15 (B) Color 5 7.5 10 15
20 25 masterbatch No. 1 Color masterbatch No. 2 (B)' Masterbatch
No. 3 Magnesium stearate* 0.33 0.48 0.63 0.90 1.15 1.39
Weight-average (A) 125,980 125,980 125,980 125,980 125,980 125,980
molecular weight (b-1) 168,000 168,000 168,000 168,000 168,000
168,000 Specific (A) 0.95 0.95 0.95 0.95 0.95 0.95 gravity (B)
and/or (B)' 0.94 0.94 0.94 0.94 0.94 0.94 Specific gravity ratio
((B) and/or (B)')/(A) 0.99 0.99 0.99 0.99 0.99 0.99 Evaluations
Ball deflection (mm) 3.36 3.36 3.35 3.35 3.35 3.34 Releasability
from mold good good good good good good Durability of markings good
good good good good fair Color uniformity good good good good good
good *The amount of magnesium stearate (component (b-4)) included
in the masterbatch is given here as the content per 100 parts by
weight of component (A) and component (b-1) combined.
TABLE-US-00004 TABLE 4 Example 7 8 9 10 Core Material B B B B
Diameter (mm) 38.55 38.55 38.55 38.55 Cover Thickness (mm) 2.07
2.07 2.07 2.07 Color yellow yellow yellow yellow Type of
masterbatch colorant dye dye dye dye Formulation (A) Himilan 1601
50 20 50 (pbw) Himilan 1557 60 80 50 Himilan 1605 40 Himilan 1706
50 Nucrel AN4319 (B) Color masterbatch No. 1 Color masterbatch No.
2 15 15 15 15 (B)' Masterbatch No. 3 Magnesium stearate* 0.90 0.90
0.90 0.90 Weight-average (A) 117,560 138,000 107,080 125,800
molecular weight (b-1) 168,000 168,000 168,000 168,000 Specific
gravity (A) 0.96 0.96 0.96 0.95 (B) and/or (B)' 0.96 0.96 0.96 0.96
Specific gravity ratio ((B) and/or (B)')/(A) 1.00 1.00 1.00 1.01
Evaluations Ball deflection (mm) 3.25 3.25 3.30 3.30 Releasability
from mold good good good good Durability of markings good good good
good Color uniformity good good good good *The amount of magnesium
stearate (component (b-4)) included in the masterbatch is given
here as the content per 100 parts by weight of component (A) and
component (b-1) combined.
TABLE-US-00005 TABLE 5 Comparative Example 1 2 3 Core Material A A
A Diameter (mm) 38.55 38.55 38.55 Cover Thickness (mm) 2.07 2.07
2.07 Color clear white yellow Type of masterbatch colorant dye
Formulation (A) Himilan 1601 42.5 42.5 (pbw) Himilan 1557 42.5 42.5
Himilan 1605 50 Himilan 1706 50 Nucrel AN4319 15 15 (B) Color
masterbatch No. 1 7.5 Color masterbatch No. 2 (B)' Masterbatch No.
3 7 3.5 Magnesium stearate* 1.86 0.90 Weight-average (A) 125,980
148,000 125,980 molecular weight (b-1) -- 61,000 133,955 Specific
gravity (A) 0.95 0.96 0.95 (B) and/or (B)' -- 1.64 1.17 Specific
gravity ratio ((B) and/or (B)')/(A) -- 1.71 1.23 Evaluations Ball
deflection (mm) 3.36 3.14 3.34 Releasability from mold NG good good
Durability of markings good NG good Color uniformity -- good NG
*The amount of magnesium stearate (component (b-4)) included in the
masterbatch is given here as the content per 100 parts by weight of
component (A) and component (b-1) combined.
[0118] Details on the ingredients shown in Tables 3 to 5 are given
below. [0119] Himilan 1601: A sodium-neutralized
ethylene-methacrylic acid copolymeric ionomer resin available from
DuPont-Mitsui Polychemicals Co., Ltd.; acid content, 10 wt %; Mw,
157,000; MFR, 1.3 g/10 min [0120] Himilan 1557: A zinc-neutralized
ethylene-methacrylic acid copolymeric ionomer resin available from
DuPont-Mitsui Polychemicals Co., Ltd.; acid content, 12 wt %; Mw,
94,600; MFR, 5.5 g/10 min [0121] Himilan 1605: A sodium-neutralized
ethylene-methacrylic acid copolymeric ionomer resin available from
DuPont-Mitsui Polychemicals Co., Ltd.; acid content, 15 wt %; Mw,
152,000; MFR, 2.8 g/10 min [0122] Himilan 1706: A zinc-neutralized
ethylene-methacrylic acid copolymeric ionomer resin available from
DuPont-Mitsui Polychemicals Co., Ltd.; acid content, 15 wt %; Mw,
144,000; MFR, 0.9 g/10 min [0123] Nucrel AN4319: An
ethylene-methacrylic acid-acrylic acid ester terpolymer available
from DuPont-Mitsui Polychemicals Co., Ltd.; Mw, 127,000; MFR, 60
g/10 min
[0124] The physical properties of the covers and golf balls
obtained in the respective Working Examples of the invention and
the Comparative Examples were evaluated based on the following
criteria. The results are shown in Table 1.
Ball Deflection:
[0125] The deflection (mm) of the ball when compressed under a
final load of 1,275 N (130 kgf) from an initial load state of 98 N
(10 kgf) was measured.
Releasability from Mold:
[0126] The ease of removing the golf ball from the mold after
molding of the ball outermost layer was rated according to the
following criteria. [0127] Good: Separation from the mold was good,
with no sticking of the molded material to the mold. [0128] NG:
Separation from the mold was poor, with some sticking of the molded
material to the mold.
Durability of Markings:
[0129] The appearance of the markings that had been printed onto
the surface of the golf ball was visually examined, in addition to
which the following abrasion test was carried out.
Abrasion Test:
[0130] Ten golf balls and 3 liters of bunker sand were placed in a
magnetic ball mill having an 8 liter capacity and mixing was
carried out for 144 hours, following which the balls were visually
examined for any loss of the markings and to assess the degree of
surface scratching, the degree of loss of luster and the degree of
sand adhesion.
[0131] The rating criteria were as follows. [0132] Good: No peeling
or loss of markings. [0133] Fair: No peeling of markings, but
slight loss of markings was observed in abrasion test. [0134] NG:
Some peeling of markings; also, significant loss of markings was
observed in abrasion test.
Color Uniformity:
[0135] The golf ball was visually examined, and the overall
appearance of the ball was rated according to the following
criteria. [0136] Good: Overall cover was uniformly colored. [0137]
NG: Color was uneven.
* * * * *