U.S. patent application number 15/292559 was filed with the patent office on 2017-06-15 for two-piece golf ball.
This patent application is currently assigned to DUNLOP SPORTS CO. LTD.. The applicant listed for this patent is DUNLOP SPORTS CO. LTD.. Invention is credited to Takahiro SAJIMA, Hironori TAKIHARA.
Application Number | 20170165529 15/292559 |
Document ID | / |
Family ID | 57136760 |
Filed Date | 2017-06-15 |
United States Patent
Application |
20170165529 |
Kind Code |
A1 |
TAKIHARA; Hironori ; et
al. |
June 15, 2017 |
TWO-PIECE GOLF BALL
Abstract
A golf ball 2 includes a core 4 and a cover 6. A value V
calculated by the following mathematical formula is equal to or
less than 1080 Hz. V=NF(2)2-2/3*NF(2)1 In the mathematical formula,
NF(2)1 represents a secondary natural frequency of the core 4, and
NF(2)2 represents a secondary natural frequency of the golf ball 2.
A difference (H1s-H1o) between a Shore C hardness H1s at a surface
of the core 4 and a Shore C hardness H1o at a central point of the
core 4 is equal to or greater than 10. An amount of compressive
deformation Df1 of the core 4 is equal to or greater than 4.1
mm.
Inventors: |
TAKIHARA; Hironori;
(Kobe-shi, JP) ; SAJIMA; Takahiro; (Kobe-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DUNLOP SPORTS CO. LTD. |
Kobe-shi |
|
JP |
|
|
Assignee: |
DUNLOP SPORTS CO. LTD.
Kobe-shi
JP
|
Family ID: |
57136760 |
Appl. No.: |
15/292559 |
Filed: |
October 13, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A63B 37/0031 20130101;
A63B 37/0083 20130101; A63B 37/0096 20130101; A63B 37/0065
20130101; A63B 37/0074 20130101; A63B 37/0033 20130101; A63B
37/0088 20130101; A63B 37/0051 20130101; A63B 37/009 20130101; A63B
37/008 20130101; A63B 37/0063 20130101; A63B 37/0094 20130101; A63B
37/0087 20130101 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 14, 2015 |
JP |
2015-242909 |
Claims
1. A two-piece golf ball including a core and a cover positioned
outside the core, wherein a value V calculated by the following
mathematical formula is equal to or less than 1080 Hz,
V=NF(2)2-2/3*NF(2)1, wherein NF(2)1 represents a secondary natural
frequency of the core, and NF(2)2 represents a secondary natural
frequency of the golf ball.
2. The two-piece golf ball according to claim 1, wherein a
difference (H1s-H1o) between a Shore C hardness H1s at a surface of
the core and a Shore C hardness H1o at a central point of the core
is equal to or greater than 10.
3. The two-piece golf ball according to claim 1, wherein the value
V is equal to or less than 1040 Hz.
4. The two-piece golf ball according to claim 3, wherein the value
V is equal to or less than 1000 Hz.
5. The two-piece golf ball according to claim 1, wherein an amount
of compressive deformation Df1 of the core is equal to or greater
than 4.1 mm.
6. The two-piece golf ball according to claim 1, wherein an amount
of compressive deformation Df2 of the two-piece golf ball is equal
to or greater than 3.5 mm.
7. The two-piece golf ball according to claim 1, wherein a
thickness T2 of the cover is equal to or greater than 0.80 mm but
equal to or less than 2.00 mm.
8. The two-piece golf ball according to claim 1, wherein a Shore D
hardness H2 of the cover is equal to or greater than 50 but equal
to or less than 65.
Description
[0001] This application claims priority on Patent Application No.
2015-242909 filed in JAPAN on Dec. 14, 2015. The entire contents of
this Japanese Patent Application are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] Field of the Invention
[0003] The present invention relates to golf balls. Specifically,
the present invention relates to so-called two-piece golf balls
including a core and a cover.
[0004] Description of the Related Art
[0005] In golf, golf balls are hit with a wood type club, an iron
type club, a hybrid type club (utility), and a putter, etc. Feel at
impact upon hitting is of interest to golf players. In general,
golf players desire golf balls having soft feel at impact.
[0006] In play by beginners, the frequency of a mishit is high.
Therefore, beginners are insensitive to feel at impact when hitting
a golf ball with a wood type club, an iron type club, or a hybrid
type club.
[0007] Meanwhile, in putting, even beginners often hit golf balls
at the sweet spots of putters. Even beginners are sensitive to feel
at impact upon putting. Beginners desire golf balls with which soft
feel at impact is obtained upon putting.
[0008] So-called thread-wound balls used to be mainstream golf
balls. At present, thread-wound balls are almost not available
commercially. In recent golf, two-piece balls, three-piece balls,
four-piece balls, five-piece balls, six-piece balls, and the like
are used.
[0009] A two-piece ball includes a core and a cover. The structure
of the two-piece ball is simple. The two-piece ball can be
manufactured at low cost. Proposals concerning two-piece balls are
disclosed in JPH11-76461 (U.S. Pat. No. 6,123,629) and U.S. Pat.
No. 5,971,870.
[0010] Upon shots by beginners, golf balls often fly in an
unintended direction. Golf balls often fall into a pond or fly into
woods. Beginners often loose golf balls. Therefore, beginners do
not prefer expensive golf balls. Two-piece balls are suitable for
beginners, since two-piece balls can be manufactured at low cost.
As descried above, beginners prefer soft feel at impact upon
putting. Improvement of feel at impact of two-piece balls upon
putting is desired.
[0011] An object of the present invention is to provide a two-piece
golf ball having excellent feel at impact upon putting.
SUMMARY OF THE INVENTION
[0012] A two-piece golf ball according to the present invention
includes a core and a cover positioned outside the core. In the
golf ball, a value V calculated by the following mathematical
formula is equal to or less than 1080 Hz.
V=NF(2)2-2/3*NF(2)1
In the mathematical formula, NF(2)1 represents a secondary natural
frequency of the core, and NF(2)2 represents a secondary natural
frequency of the golf ball.
[0013] The two-piece golf ball according to the present invention
has a simple structure. The golf ball can be manufactured at low
cost. Since the value V is equal to or less than 1080 Hz, the feel
at impact of the golf ball upon putting is soft. The golf ball can
achieve both a low price and desired feel at impact.
[0014] Preferably, a difference (H1s-H1o) between a Shore C
hardness H1s at a surface of the core and a Shore C hardness H1o at
a central point of the core is equal to or greater than 10.
[0015] Preferably, the value V is equal to or less than 1040 Hz.
Further preferably, the value V is equal to or less than 1000
Hz.
[0016] Preferably, an amount of compressive deformation Df1 of the
core is equal to or greater than 4.1 mm.
[0017] Preferably, an amount of compressive deformation Df2 of the
two-piece golf ball is equal to or greater than 3.5 mm.
[0018] Preferably, a thickness T2 of the cover is equal to or
greater than 0.80 mm but equal to or less than 2.00 mm. Preferably,
a Shore D hardness H2 of the cover is equal to or greater than 50
but equal to or less than 65.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a cross-sectional view of a golf ball according to
one embodiment of the present invention;
[0020] FIG. 2 is a conceptual diagram showing a device for
measuring a natural frequency of the golf ball in FIG. 1; and
[0021] FIG. 3 is a graph showing a relationship between a secondary
natural frequency NF(2)1 of a core and a secondary natural
frequency NF(2)2 of the golf ball.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The following will describe in detail the present invention
based on preferred embodiments with appropriate reference to the
drawings.
[0023] A golf ball 2 shown in FIG. 1 includes a spherical core 4
and a cover 6 positioned outside the core 4. In the present
embodiment, the cover 6 is joined directly to the core 4. The golf
ball 2 is a so-called two-piece ball. The golf ball 2 has a
plurality of dimples 8 on the surface thereof. Of the surface of
the golf ball 2, a part other than the dimples 8 is a land 10. The
golf ball 2 includes a paint layer and a mark layer on the external
side of the cover 6 although these layers are not shown in the
drawing.
[0024] The golf ball 2 preferably has a diameter of equal to or
greater than 40 mm but equal to or less than 45 mm. From the
standpoint of conformity to the rules established by the United
States Golf Association (USGA), the diameter is particularly
preferably equal to or greater than 42.67 mm. In light of
suppression of air resistance, the diameter is more preferably
equal to or less than 44 mm and particularly preferably equal to or
less than 42.80 mm. The golf ball 2 preferably has a weight of
equal to or greater than 40 g but equal to or less than 50 g. In
light of attainment of great inertia, the weight is more preferably
equal to or greater than 44 g and particularly preferably equal to
or greater than 45.00 g. From the standpoint of conformity to the
rules established by the USGA, the weight is particularly
preferably equal to or less than 45.93 g.
[0025] The core 4 is formed by crosslinking a rubber composition.
Examples of preferable base rubbers for use in the rubber
composition include polybutadienes, polyisoprenes,
styrene-butadiene copolymers, ethylene-propylene-diene copolymers,
and natural rubbers. In light of resilience performance,
polybutadienes are preferable. When a polybutadiene and another
rubber are used in combination, it is preferred if the
polybutadiene is a principal component. Specifically, the
proportion of the polybutadiene to the entire base rubber is
preferably equal to or greater than 50% by weight and particularly
preferably equal to or greater than 80% by weight. A polybutadiene
in which the proportion of cis-1,4 bonds is equal to or greater
than 80% is particularly preferable.
[0026] The rubber composition of the core 4 preferably includes a
co-crosslinking agent. Preferable co-crosslinking agents in light
of resilience performance of the golf ball 2 are monovalent or
bivalent metal salts of an .alpha.,.beta.-unsaturated carboxylic
acid having 2 to 8 carbon atoms. Examples of preferable
co-crosslinking agents include zinc acrylate, magnesium acrylate,
zinc methacrylate, and magnesium methacrylate. In light of
resilience performance of the golf ball 2, zinc acrylate and zinc
methacrylate are particularly preferable.
[0027] The rubber composition may include a metal oxide and an
.alpha.,.beta.-unsaturated carboxylic acid having 2 to 8 carbon
atoms. They both react with each other in the rubber composition to
obtain a salt. The salt serves as a co-crosslinking agent. Examples
of preferable .alpha.,.beta.-unsaturated carboxylic acids include
acrylic acid and methacrylic acid. Examples of preferable metal
oxides include zinc oxide and magnesium oxide.
[0028] The amount of the co-crosslinking agent per 100 parts by
weight of the base rubber is preferably equal to or greater than 10
parts by weight. The golf ball 2 that includes the core 4 in which
this amount is equal to or greater than 10 parts by weight has
excellent resilience performance. In this respect, this amount is
more preferably equal to or greater than 15 parts by weight and
particularly preferably equal to or greater than 20 parts by
weight.
[0029] The amount of the co-crosslinking agent per 100 parts by
weight of the base rubber is preferably equal to or less than 40
parts by weight. The golf ball 2 that includes the core 4 in which
this amount is equal to or less than 40 parts by weight has soft
feel at impact upon putting. In this respect, this amount is more
preferably equal to or less than 35 parts by weight and
particularly preferably equal to or less than 30 parts by
weight.
[0030] Preferably, the rubber composition of the core 4 includes an
organic peroxide. The organic peroxide serves as a crosslinking
initiator. The organic peroxide contributes to the resilience
performance of the golf ball 2. Examples of suitable organic
peroxides include dicumyl peroxide,
1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,
2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide.
An organic peroxide with particularly high versatility is dicumyl
peroxide.
[0031] The amount of the organic peroxide per 100 parts by weight
of the base rubber is preferably equal to or greater than 0.1 parts
by weight. The golf ball 2 that includes the core 4 in which this
amount is equal to or greater than 0.1 parts by weight has
excellent resilience performance. In this respect, this amount is
more preferably equal to or greater than 0.3 parts by weight and
particularly preferably equal to or greater than 0.5 parts by
weight.
[0032] The amount of the organic peroxide per 100 parts by weight
of the base rubber is preferably equal to or less than 3.0 parts by
weight. The golf ball 2 that includes the core 4 in which this
amount is equal to or less than 3.0 parts by weight has soft feel
at impact upon putting. In this respect, this amount is more
preferably equal to or less than 2.5 parts by weight and
particularly preferably equal to or less than 2.0 parts by
weight.
[0033] The rubber composition of the core 4 includes an organic
sulfur compound. Organic sulfur compounds include naphthalenethiol
compounds, benzenethiol compounds, and disulfide compounds.
[0034] Examples of naphthalenethiol compounds include
1-naphthalenethiol, 2-naphthalenethiol,
4-chloro-1-naphthalenethiol, 4-bromo-1-naphthalenethiol,
1-chloro-2-naphthalenethiol, 1-bromo-2-naphthalenethiol,
1-fluoro-2-naphthalenethiol, 1-cyano-2-naphthalenethiol, and
1-acetyl-2-naphthalenethiol.
[0035] Examples of benzenethiol compounds include benzenethiol,
4-chlorobenzenethiol, 3-chlorobenzenethiol, 4-bromobenzenethiol,
3-bromobenzenethiol, 4-fluorobenzenethiol, 4-iodobenzenethiol,
2,5-dichlorobenzenethiol, 3,5-dichlorobenzenethiol,
2,6-dichlorobenzenethiol, 2,5-dibromobenzenethiol,
3,5-dibromobenzenethiol, 2-chloro-5-bromobenzenethiol,
2,4,6-trichlorobenzenethiol, 2,3,4,5,6-pentachlorobenzenethiol,
2,3,4,5,6-pentafluorobenzenethiol, 4-cyanobenzenethiol,
2-cyanobenzenethiol, 4-nitrobenzenethiol, and
2-nitrobenzenethiol.
[0036] Examples of disulfide compounds include diphenyl disulfide,
bis(4-chlorophenyl)disulfide, bis(3-chlorophenyl)disulfide,
bis(4-bromophenyl)disulfide, bis(3-bromophenyl)disulfide,
bis(4-fluorophenyl)disulfide, bis(4-iodophenyl)disulfide,
bis(4-cyanophenyl)disulfide, bis(2,5-dichlorophenyl)disulfide,
bis(3,5-dichlorophenyl)disulfide, bis(2,6-dichlorophenyl)disulfide,
bis(2,5-dibromophenyl)disulfide, bis(3,5-dibromophenyl)disulfide,
bis(2-chloro-5-bromophenyl)disulfide,
bis(2-cyano-5-bromophenyl)disulfide,
bis(2,4,6-trichlorophenyl)disulfide,
bis(2-cyano-4-chloro-6-bromophenyl)disulfide,
bis(2,3,5,6-tetrachlorophenyl)disulfide,
bis(2,3,4,5,6-pentachlorophenyl)disulfide, and
bis(2,3,4,5,6-pentabromophenyl)disulfide.
[0037] In light of resilience performance of the golf ball 2, the
amount of the organic sulfur compound per 100 parts by weight of
the base rubber is preferably equal to or greater than 0.1 parts by
weight and particularly preferably equal to or greater than 0.2
parts by weight. In light of feel at impact upon putting, the
amount is preferably equal to or less than 1.5 parts by weight,
more preferably equal to or less than 1.0 parts by weight, and
particularly preferably equal to or less than 0.8 parts by weight.
Two or more organic sulfur compounds may be used in
combination.
[0038] The rubber composition of the core 4 may include a filler
for the purpose of specific gravity adjustment and the like.
Examples of suitable fillers include zinc oxide, barium sulfate,
calcium carbonate, and magnesium carbonate. The amount of the
filler is determined as appropriate so that the intended specific
gravity of the core 4 is accomplished.
[0039] The rubber composition may include various additives, such
as sulfur, a carboxylic acid, a carboxylate, an anti-aging agent, a
coloring agent, a plasticizer, a dispersant, and the like, in an
adequate amount. The rubber composition may include crosslinked
rubber powder or synthetic resin powder.
[0040] The core 4 preferably has a diameter of equal to or greater
than 39.0 mm. In the golf ball 2 that includes the core 4 having a
diameter of equal to or greater than 39.0 mm, the cover 6 is thin.
Therefore, with the golf ball 2, the feel at impact upon putting is
soft. Furthermore, the golf ball 2 has excellent resilience
performance. In these respects, the diameter is more preferably
equal to or greater than 39.3 mm and particularly preferably equal
to or greater than 39.5 mm. In light of durability of the golf ball
2, the diameter is preferably equal to or less than 41.0 mm, more
preferably equal to or less than 40.6 mm, and particularly
preferably equal to or less than 40.2 mm.
[0041] The core 4 preferably has an amount of compressive
deformation Df1 of equal to or greater than 4.1 mm. With the core 4
having an amount of compressive deformation Df1 of equal to or
greater than 4.1 mm, the feel at impact upon putting is soft. In
this respect, the amount of compressive deformation Df1 is more
preferably equal to or greater than 4.2 mm and particularly
preferably equal to or greater than 4.4 mm. In light of resilience
performance of the golf ball 2, the amount of compressive
deformation Df1 is preferably equal to or less than 6.5 mm, more
preferably equal to or less than 6.0 mm, and particularly
preferably equal to or less than 5.5 mm.
[0042] For measurement of the amount of compressive deformation, a
YAMADA type compression tester is used. In the tester, a sphere
(the core 4 or the golf ball 2) is placed on a hard plate made of
metal. Next, a cylinder made of metal gradually descends toward the
sphere. The sphere, squeezed between the bottom face of the
cylinder and the hard plate, becomes deformed. A migration distance
of the cylinder, starting from the state in which an initial load
of 98 N is applied to the sphere up to the state in which a final
load of 1274 N is applied thereto, is measured. A moving speed of
the cylinder until the initial load is applied is 0.83 mm/s. A
moving speed of the cylinder after the initial load is applied
until the final load is applied is 1.67 mm/s.
[0043] The difference (H1s-H1o) between a Shore C hardness H1s at
the surface of the core 4 and a Shore C hardness H1o at the central
point of the core 4 is preferably equal to or greater than 10. The
core 4 having a difference (H1s-H1o) of equal to or greater than 10
has a so-called outer-hard/inner-soft structure. When the golf ball
2 including the core 4 is hit with a driver, the spin is
suppressed. When the golf ball 2 including the core 4 is hit with a
driver, a high launch angle is obtained.
[0044] Upon a shot with a driver, an appropriate trajectory height
and appropriate flight duration are required. With the golf ball 2
that achieves a desired trajectory height and desired flight
duration at a high spin rate, the run after landing is short. With
the golf ball 2 that achieves a desired trajectory height and
desired flight duration at a high launch angle, the run after
landing is long. In light of flight distance, the golf ball 2 that
achieves a desired trajectory height and desired flight duration at
a high launch angle is preferable. The core 4 having an
outer-hard/inner-soft structure can contribute to a high launch
angle and a low spin rate as described above. Although the amount
of compressive deformation Df1 is small, the core 4 can contribute
to the flight performance of the golf ball 2.
[0045] In light of flight performance, the difference (H1s-H1o) is
more preferably equal to or greater than 11 and particularly
preferably equal to or greater than 12. In light of durability of
the golf ball 2, the difference (H1s-H1o) is preferably equal to or
less than 30, more preferably equal to or less than 28, and
particularly preferably equal to or less than 25.
[0046] In light of durability and resilience performance, the
central hardness H1o is preferably equal to or greater than 40,
more preferably equal to or greater than 45, and particularly
preferably equal to or greater than 50. In light of spin
suppression, the hardness H1o is preferably equal to or less than
70, more preferably equal to or less than 65, and particularly
preferably equal to or less than 60.
[0047] The hardness H1o is measured with a Shore C type hardness
scale mounted to an automated hardness meter (trade name "digi test
II" manufactured by Heinrich Bareiss Prufgeratebau GmbH). The
hardness scale is pressed against the central point of the
cross-section of a hemisphere obtained by cutting the golf ball 2.
The measurement is conducted in the environment of 23.degree.
C.
[0048] In light of spin suppression, the surface hardness H1s is
preferably equal to or greater than 64, more preferably equal to or
greater than 66, and particularly preferably equal to or greater
than 68. In light of durability of the golf ball 2, the hardness
H1s is preferably equal to or less than 85, more preferably equal
to or less than 83, and particularly preferably equal to or less
than 80.
[0049] The hardness H1s is measured with a Shore C type hardness
scale mounted to an automated hardness meter (trade name "digi test
II" manufactured by Heinrich Bareiss Prufgeratebau GmbH). The
hardness scale is pressed against the surface of the core 4. The
measurement is conducted in the environment of 23.degree. C.
[0050] The core 4 preferably has a weight of equal to or greater
than 10 g but equal to or less than 42 g. The temperature for
crosslinking the core 4 is equal to or higher than 140.degree. C.
but equal to or lower than 180.degree. C. The time period for
crosslinking the core 4 is equal to or longer than 10 minutes but
equal to or shorter than 60 minutes.
[0051] The cover 6 is positioned outside the core 4. The cover 6 is
the outermost layer except the mark layer and the paint layer. The
cover 6 is formed from a thermoplastic resin composition. Examples
of the base polymer of the resin composition include ionomer
resins, thermoplastic polyester elastomers, thermoplastic polyamide
elastomers, thermoplastic polyurethane elastomers, thermoplastic
polyolefin elastomers, and thermoplastic polystyrene elastomers.
Ionomer resins are particularly preferable. Ionomer resins are
highly elastic. The golf ball 2 that includes the cover 6 including
an ionomer resin has excellent resilience performance. The cover 6
may be formed from a thermosetting resin composition.
[0052] An ionomer resin and another resin may be used in
combination. In this case, in light of resilience performance, the
ionomer resin is included as the principal component of the base
polymer. The proportion of the ionomer resin to the entire base
polymer is preferably equal to or greater than 50% by weight, more
preferably equal to or greater than 70% by weight, and particularly
preferably equal to or greater than 85% by weight.
[0053] Examples of preferable ionomer resins include binary
copolymers formed with an .alpha.-olefin and an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms. A preferable binary copolymer includes 80% by weight or more
but 90% by weight or less of an .alpha.-olefin, and 10% by weight
or more but 20% by weight or less of an .alpha.,.beta.-unsaturated
carboxylic acid. The binary copolymer has excellent resilience
performance. Examples of other preferable ionomer resins include
ternary copolymers formed with: an .alpha.-olefin; an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms; and an .alpha.,.beta.-unsaturated carboxylate ester having 2
to 22 carbon atoms. A preferable ternary copolymer includes 70% by
weight or more but 85% by weight or less of an .alpha.-olefin, 5%
by weight or more but 30% by weight or less of an
.alpha.,.beta.-unsaturated carboxylic acid, and 1% by weight or
more but 25% by weight or less of an .alpha.,.beta.-unsaturated
carboxylate ester. The ternary copolymer has excellent resilience
performance. For the binary copolymer and the ternary copolymer,
preferable .alpha.-olefins are ethylene and propylene, while
preferable .alpha.,.beta.-unsaturated carboxylic acids are acrylic
acid and methacrylic acid. A particularly preferable ionomer resin
is a copolymer formed with ethylene and acrylic acid. Another
particularly preferable ionomer resin is a copolymer formed with
ethylene and methacrylic acid.
[0054] In the binary copolymer and the ternary copolymer, some of
the carboxyl groups are neutralized with metal ions. Examples of
metal ions for use in neutralization include sodium ion, potassium
ion, lithium ion, zinc ion, calcium ion, magnesium ion, aluminum
ion, and neodymium ion. The neutralization may be carried out with
two or more types of metal ions. Particularly suitable metal ions
in light of resilience performance and durability of the golf ball
2 are sodium ion, zinc ion, lithium ion, and magnesium ion.
[0055] Specific examples of ionomer resins include trade names
"Himilan 1555", "Himilan 1557", "Himilan 1605", "Himilan 1706",
"Himilan 1707", "Himilan 1856", "Himilan 1855", "Himilan AM7311",
"Himilan AM7315", "Himilan AM7317", "Himilan AM7329", and "Himilan
AM7337", manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.;
trade names "Surlyn 6120", "Surlyn 6910", "Surlyn 7930", "Surlyn
7940", "Surlyn 8140", "Surlyn 8150", "Surlyn 8940", "Surlyn 8945",
"Surlyn 9120", "Surlyn 9150", "Surlyn 9910", "Surlyn 9945", "Surlyn
AD8546", "HPF1000", and "HPF2000", manufactured by E.I. du Pont de
Nemours and Company; and trade names "IOTEK 7010", "IOTEK 7030",
"IOTEK 7510", "IOTEK 7520", "IOTEK 8000", and "IOTEK 8030",
manufactured by ExxonMobil Chemical Corporation. Two or more
ionomer resins may be used in combination.
[0056] The resin composition of the cover 6 may include a styrene
block-containing thermoplastic elastomer. The styrene
block-containing thermoplastic elastomer includes a polystyrene
block as a hard segment, and a soft segment. A typical soft segment
is a diene block. Examples of compounds for the diene block include
butadiene, isoprene, 1,3-pentadiene, and
2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferable.
Two or more compounds may be used in combination.
[0057] Examples of styrene block-containing thermoplastic
elastomers include styrene-butadiene-styrene block copolymers
(SBS), styrene-isoprene-styrene block copolymers (SIS),
styrene-isoprene-butadiene-styrene block copolymers (SIBS),
hydrogenated SBS, hydrogenated SIS, and hydrogenated SIBS. Examples
of hydrogenated SBS include styrene-ethylene-butylene-styrene block
copolymers (SEBS). Examples of hydrogenated SIS include
styrene-ethylene-propylene-styrene block copolymers (SEPS).
Examples of hydrogenated SIBS include
styrene-ethylene-ethylene-propylene-styrene block copolymers
(SEEPS).
[0058] In light of resilience performance of the golf ball 2, the
content of the styrene component in the styrene block-containing
thermoplastic elastomer is preferably equal to or greater than 10%
by weight, more preferably equal to or greater than 12% by weight,
and particularly preferably equal to or greater than 15% by weight.
In light of feel at impact of the golf ball 2, the content is
preferably equal to or less than 50% by weight, more preferably
equal to or less than 47% by weight, and particularly preferably
equal to or less than 45% by weight.
[0059] In the present invention, styrene block-containing
thermoplastic elastomers include an alloy of an olefin and one or
more members selected from the group consisting of SBS, SIS, SIBS,
SEBS, SEPS, and SEEPS. The olefin component in the alloy is
presumed to contribute to improvement of compatibility with another
base polymer. The alloy can contribute to the resilience
performance of the golf ball 2. An olefin having 2 to 10 carbon
atoms is preferable. Examples of suitable olefins include ethylene,
propylene, butene, and pentene. Ethylene and propylene are
particularly preferable.
[0060] Specific examples of polymer alloys include trade names
"RABALON T3221C", "RABALON T3339C", "RABALON SJ4400N", "RABALON
SJ5400N", "RABALON SJ6400N", "RABALON SJ7400N", "RABALON SJ8400N",
"RABALON SJ9400N", and "RABALON SR04", manufactured by Mitsubishi
Chemical Corporation. Other specific examples of styrene
block-containing thermoplastic elastomers include trade name
"Epofriend A1010" manufactured by Daicel Chemical Industries, Ltd.,
and trade name "SEPTON HG-252" manufactured by Kuraray Co.,
Ltd.
[0061] In light of feel at impact upon putting, the proportion of
the styrene block-containing thermoplastic elastomer to the entire
base polymer is preferably equal to or greater than 2% by weight,
more preferably equal to or greater than 4% by weight, and
particularly preferably equal to or greater than 6% by weight. In
light of spin suppression, the proportion is preferably equal to or
less than 30% by weight, more preferably equal to or less than 25%
by weight, and particularly preferably equal to or less than 20% by
weight.
[0062] The resin composition of the cover 6 may include a coloring
agent, a filler, a dispersant, an antioxidant, an ultraviolet
absorber, a light stabilizer, a fluorescent material, a fluorescent
brightener, and the like in an adequate amount. When the hue of the
golf ball 2 is white, a typical coloring agent is titanium
dioxide.
[0063] The cover 6 preferably has a thickness T2 of equal to or
less than 2.00 mm. The cover 6 having a thickness T2 of equal to or
less than 2.00 mm does not impair soft feel at impact upon putting.
In this respect, the thickness T2 is more preferably equal to or
less than 1.85 mm and particularly preferably equal to or less than
1.70 mm. In light of ease of forming the cover 6 and in light of
durability of the golf ball 2, the thickness T2 is preferably equal
to or greater than 0.80 mm, more preferably equal to or greater
than 0.95 mm, and particularly preferably equal to or greater than
1.05 mm. The thickness T2 is measured at a position immediately
below the land 10.
[0064] From the standpoint that the golf ball 2 can have an
outer-hard/inner-soft structure as a whole, the cover 6 has a Shore
D hardness H2 of preferably equal to or greater than 50, more
preferably equal to or greater than 53, and particularly preferably
equal to or greater than 55. In light of feel at impact upon
putting, the hardness H2 is preferably equal to or less than 65,
more preferably equal to or less than 63, and particularly
preferably equal to or less than 61.
[0065] The hardness H2 of the cover 6 is measured according to the
standards of "ASTM-D 2240-68". The hardness H2 is measured with a
Shore D type hardness scale mounted to an automated hardness meter
(trade name "digi test II" manufactured by Heinrich Bareiss
Prufgeratebau GmbH). For the measurement, a sheet that is formed by
hot press, is formed from the same material as that of the cover 6,
and has a thickness of about 2 mm is used. Prior to the
measurement, a sheet is kept at 23.degree. C. for two weeks. At the
measurement, three sheets are stacked.
[0066] The golf ball 2 preferably has an amount of compressive
deformation Df2 of equal to or greater than 3.5 mm. With the golf
ball 2 having an amount of compressive deformation Df2 of equal to
or greater than 3.5 mm, the feel at impact upon putting is soft. In
this respect, the amount of compressive deformation Df2 is more
preferably equal to or greater than 3.6 mm and particularly
preferably equal to or greater than 3.8 mm. In light of resilience
performance of the golf ball 2, the amount of compressive
deformation Df2 is preferably equal to or less than 6.0 mm, more
preferably equal to or less than 5.5 mm, and particularly
preferably equal to or less than 5.0 mm.
[0067] FIG. 2 shows a device for measuring natural frequencies of
the core 4 and the golf ball 2. The device includes a vibration
exciter 12, a plate 14, a first acceleration pickup 16, and a
second acceleration pickup 18. The plate 14 is mounted on the
vibration exciter 12. A sphere (the core 4 or the golf ball 2) is
placed on the plate 14. The first acceleration pickup 16 is mounted
on the plate 14. The second acceleration pickup 18 is mounted on
the sphere. Vibration is applied to the sphere by the vibration
exciter 12. A signal of acceleration applied to the sphere is
outputted from the first acceleration pickup 16. A signal of the
acceleration of the sphere is outputted from the second
acceleration pickup 18. These signals are inputted into a dynamic
signal analyzer. By calculation of the analyzer, a curve is
obtained which shows a relationship between frequency and
mechanical impedance at the sphere. The frequency at a minimum
point of the curve is a natural frequency. The frequency at a
minimum point that appears first on the curve is a primary natural
frequency. The frequency at a minimum point that appears second on
the curve is a secondary natural frequency. The vibration exciter
12 is typically trade name "PET", manufactured by IMV Corporation.
The dynamic signal analyzer is typically trade name "HP-5420A",
manufactured by Yokokawa Hewlett-Packard, Ltd.
[0068] As a result of thorough research, the present inventors have
found that soft feel at impact upon putting is achieved when a
secondary natural frequency NF(2)1 of the core 4 and a secondary
natural frequency NF(2)2 of the golf ball 2 have a predetermined
relationship.
[0069] FIG. 3 is a graph showing a relationship between the
secondary natural frequency NF(2)1 of the core 4 and the secondary
natural frequency NF(2)2 of the golf ball 2. In this graph, the
horizontal axis indicates the secondary natural frequency NF(2)1 of
the core, and the vertical axis indicates the secondary natural
frequency NF(2)2 of the golf ball. A straight line indicated by
reference sign L1 in this graph is represented by the following
mathematical formula.
NF(2)2=2/3*NF(2)1+1080
In the zone below the straight line L1 in this graph, a value V
calculated by the following mathematical formula is equal to or
less than 1080 Hz.
V=NF(2)2-2/3*NF(2)1
According to the finding by the present inventors, the golf ball 2
having a value V of equal to or less than 1080 Hz has excellent
feel at impact upon putting. With the golf ball 2, the feel at
impact upon putting is soft.
[0070] A straight line indicated by reference sign L2 in the graph
of FIG. 3 is represented by the following mathematical formula.
NF(2)2=2/3*NF(2)1+1040
In the zone below the straight line L2 in this graph, the value V
is equal to or less than 1040 Hz. The golf ball 2 having a value V
of equal to or less than 1040 Hz has excellent feel at impact upon
putting. With the golf ball 2, the feel at impact upon putting is
soft.
[0071] A straight line indicated by reference sign L3 in the graph
of FIG. 3 is represented by the following mathematical formula.
NF(2)2=2/3*NF(2)1+1000
In the zone below the straight line L3 in this graph, the value V
is equal to or less than 1000 Hz. The golf ball 2 having a value V
of equal to or less than 1000 Hz has excellent feel at impact upon
putting. With the golf ball 2, the feel at impact upon putting is
soft.
[0072] In light of durability and resilience performance of the
golf ball 2, the value V is preferably equal to or greater than 800
Hz.
EXAMPLES
Example 1
[0073] A rubber composition A was obtained by kneading 100 parts by
weight of a high-cis polybutadiene (trade name "BR-730",
manufactured by JSR Corporation), 22.0 parts by weight of zinc
diacrylate, 5 parts by weight of zinc oxide, an appropriate amount
of barium sulfate, 0.5 parts by weight of diphenyl disulfide, and
0.9 parts by weight of dicumyl peroxide. This rubber composition A
was placed into a mold including upper and lower mold halves each
having a hemispherical cavity, and heated at 160.degree. C. for 20
minutes to obtain a core with a diameter of 39.8 mm. The amount of
barium sulfate was adjusted such that the weight of a golf ball was
appropriate.
[0074] A resin composition a was obtained by kneading 47 parts by
weight of an ionomer resin (the aforementioned "Himilan 1555"), 46
parts by weight of another ionomer resin (the aforementioned
"Himilan 1557"), 7 parts by weight of a styrene block-containing
thermoplastic elastomer (the aforementioned "RABALON T3221C"), 4
parts by weight of titanium dioxide, and 0.2 parts by weight of a
light stabilizer (trade name "JF-90", manufactured by Johoku
Chemical Co., Ltd.) with a twin-screw kneading extruder. The core
was placed into a final mold that includes upper and lower mold
halves each having a hemispherical cavity. The final mold has a
large number of pimples on the cavity face thereof. By injection
molding, the melted resin composition a was injected around the
core to form a cover with a thickness T2 of 1.45 mm. Dimples having
a shape that is the inverted shape of the pimples were formed on
the cover.
[0075] A clear paint including a two-component curing type
polyurethane as a base material was applied to this cover to obtain
a golf ball of Example 1 with a diameter of about 42.7 mm and a
weight of about 45.6 g.
Examples 2 to 11 and Comparative Examples 1 to 3
[0076] Golf balls of Examples 2 to 11 and Comparative Examples 1 to
3 were obtained in the same manner as Example 1, except the
specifications of the core and the cover were as shown in Tables 4
to 6 below. The specifications of the core are shown in detail in
Tables 1 and 2 below. The specifications of the cover are shown in
detail in Table 3 below.
[0077] [Flight Test]
[0078] A driver (trade name "XXIO8", manufactured by DUNLOP SPORTS
CO. LTD., shaft hardness: R, loft angle: 10.5.degree.) was attached
to a swing machine manufactured by Golf Laboratories, Inc. A golf
ball was hit under a condition of a head speed of 40 m/sec, and the
ball initial speed, the spin rate, and the flight distance were
measured. The flight distance is the distance between the point at
the hit and the point at which the golf ball stopped. The average
value of values obtained by 12 measurements is shown in Tables 4 to
6 below.
[0079] [Feel at Impact]
[0080] Twenty golf players hit golf balls with putters and were
asked about feeling. The evaluation was categorized as follows on
the basis of the number of golf players who answered, "the feeling
was favorable".
[0081] A: 16 to 20
[0082] B: 10 to 15
[0083] C: 3 to 9
[0084] D: 0 to 2
The results are shown in Tables 4 to 6 below.
TABLE-US-00001 TABLE 1 Specifications of Core (parts by weight) A B
C D Polybutadiene 100 100 100 100 Zinc oxide 5 5 5 5 Zinc acrylate
22.0 24.8 21.6 21.2 Barium sulfate * * * * Diphenyl disulfide 0.5
0.5 0.5 0.5 Dicumyl peroxide 0.9 0.9 0.9 0.9 2-naphthalenethiol --
-- -- -- Crosslinking 160 160 160 160 temperature (.degree. C.)
Crosslinking time 20 20 20 20 period (min) * Appropriate amount
TABLE-US-00002 TABLE 2 Specifications of Core (parts by weight) E F
G H Polybutadiene 100 100 100 100 Zinc oxide 5 5 5 5 Zinc acrylate
20.8 26.0 21.0 27.0 Barium sulfate * * * * Diphenyl disulfide 0.5
0.5 0.5 0.5 Dicumyl peroxide 0.9 0.9 0.9 0.8 2-naphthalenethiol --
-- -- 0.1 Crosslinking 160 160 140 160 temperature (.degree. C.)
Crosslinking time 20 20 20 20 period (min) * Appropriate amount
TABLE-US-00003 TABLE 3 Specifications of Cover (parts by weight) a
b c d Himilan 1555 47 -- -- Himilan AM7329 -- 40 40 50 Himilan 1557
46 -- -- -- Himilan 1605 -- 52 57 47 RABALON T3221C 7 8 3 3
Titanium dioxide 4 4 4 4 JF-90 0.2 0.2 0.2 0.2 H2 (Shore D) 57 59
61 63
TABLE-US-00004 TABLE 4 Results of Evaluation Ex. 1 Ex. 2 Ex. 3 Ex.
4 Ex. 5 Core Composition A B C D E Diameter (mm) 39.8 39.8 39.8
39.8 39.8 Df1 (mm) 4.85 4.15 4.95 5.05 5.15 H1o (shore C) 58 62 57
56 55 H1s (shore C) 72 76 71 70 69 H1s - H1o 14 14 14 14 14 NF(2)1
(Hz) 1355 1631 1315 1275 1235 Cover Composition a a b c d T2 (mm)
1.45 1.45 1.45 1.45 1.45 H2 (Shore D) 57 57 59 61 63 Ball NF(2)2
(Hz) 1855 2031 1865 1875 1885 Df2 (mm) 4.25 3.65 4.25 4.25 4.25 V
(Hz) 952 944 988 1025 1062 Feel at impact A B A B C Flight test
Spin (rpm) 2500 2588 2450 2400 2350 Initial speed (m/s) 57.50 57.70
57.63 57.76 57.89 Flight distance (m) 195.9 196.0 196.9 198.0
199.0
TABLE-US-00005 TABLE 5 Results of Evaluation Ex. 6 Ex. 7 Ex. 8 Ex.
9 Ex. 10 Core Composition A B F C G Diameter (mm) 39.5 39.5 39.5
39.5 40.2 Df1 (mm) 4.85 4.15 3.85 4.95 4.75 H1o (shore C) 58 62 64
57 60 H1s (shore C) 72 76 78 71 68 H1s - H1o 14 14 14 14 8 NF(2)1
(Hz) 1347 1623 1761 1307 1316 Cover Composition a a a b a T2 (mm)
1.60 1.60 1.60 1.60 1.25 H2 (Shore D) 57 57 57 59 57 Ball NF(2)2
(Hz) 1927 2103 2191 1937 1816 Df2 (mm) 4.23 3.63 3.38 4.23 4.27 V
(Hz) 1029 1021 1017 1066 939 Feel at impact A B C B A Flight test
Spin (rpm) 2520 2608 2683 2470 2650 Initial speed (m/s) 57.52 57.72
57.82 57.65 57.48 Flight distance (m) 195.8 195.9 195.7 196.8
194.4
TABLE-US-00006 TABLE 6 Results of Evaluation Comp. Comp. Comp. Ex.
11 Ex. 1 Ex. 2 Ex. 3 Core Composition G D A H Diameter (mm) 39.5
39.5 39.1 39.5 Df1 (mm) 4.75 5.05 4.85 4.00 H1o (shore C) 60 56 58
58 H1s (shore C) 68 70 72 78 H1s - H1o 8 14 14 20 NF(2)1 (Hz) 1304
1267 1507 1779 Cover Composition a c a a T2 (mm) 1.60 1.60 1.80
1.60 H2 (Shore D) 57 61 57 57 Ball NF(2)2 (Hz) 1834 1947 2167 2269
Df2 (mm) 4.23 4.23 4.21 3.66 V (Hz) 965 1102 1162 1083 Feel at
impact A D D D Flight test Spin (rpm) 2685 2420 2540 2618 Initial
speed (m/s) 57.52 57.78 57.54 58.29 Flight distance (m) 194.3 197.9
195.7 198.4
[0085] As shown in Tables 4 to 6, the golf ball of each Example has
excellent feel at impact upon putting and has excellent flight
performance upon a shot with a driver. From the results of
evaluation, advantages of the present invention are clear.
[0086] The golf ball according to the present invention is suitable
for, for example, playing golf on golf courses and practicing at
driving ranges. The above descriptions are merely illustrative
examples, and various modifications can be made without departing
from the principles of the present invention.
* * * * *