U.S. patent application number 13/632494 was filed with the patent office on 2013-04-18 for solid golf ball.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. The applicant listed for this patent is BRIDGESTONE SPORTS CO., LTD.. Invention is credited to Daisuke ARAI, Hiroshi HIGUCHI, Takashi OHIRA, Yuichiro OZAWA, Katsunori SATO.
Application Number | 20130095955 13/632494 |
Document ID | / |
Family ID | 48086358 |
Filed Date | 2013-04-18 |
United States Patent
Application |
20130095955 |
Kind Code |
A1 |
HIGUCHI; Hiroshi ; et
al. |
April 18, 2013 |
SOLID GOLF BALL
Abstract
The invention provides a solid golf ball having a core and a
cover, the core being formed of a rubber composition containing a
base rubber, a co-crosslinking agent, a crosslinking initiator and
a metal oxide. The base rubber is a mixture of polybutadiene and a
styrene-butadiene rubber, the styrene-butadiene rubber having a
styrene bond content of not more than 35 wt %. The co-crosslinking
agent is methacrylic acid. The core deflection under specific
loading and the VR value for dimples on the ball surface are set
within specific ranges.
Inventors: |
HIGUCHI; Hiroshi;
(Chichibushi, JP) ; OHIRA; Takashi; (Chichibushi,
JP) ; ARAI; Daisuke; (Chichibushi, JP) ;
OZAWA; Yuichiro; (Chichibushi, JP) ; SATO;
Katsunori; (Chichibushi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BRIDGESTONE SPORTS CO., LTD.; |
Tokyo |
|
JP |
|
|
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Family ID: |
48086358 |
Appl. No.: |
13/632494 |
Filed: |
October 1, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13351790 |
Jan 17, 2012 |
|
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13632494 |
|
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Current U.S.
Class: |
473/372 |
Current CPC
Class: |
A63B 37/0017 20130101;
A63B 37/0016 20130101; A63B 37/0074 20130101; A63B 37/0018
20130101; A63B 37/0029 20130101; A63B 37/0031 20130101; A63B
37/0066 20130101; A63B 37/0068 20130101; A63B 37/0054 20130101;
A63B 37/0051 20130101; A63B 37/0084 20130101; A63B 37/0021
20130101; A63B 37/0033 20130101; A63B 37/0065 20130101; A63B 37/002
20130101 |
Class at
Publication: |
473/372 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 27, 2011 |
JP |
2011-099969 |
Claims
1. A solid golf ball comprising a core and a cover, the core being
formed of a rubber composition comprising a base rubber, a
co-crosslinking agent, a crosslinking initiator and a metal oxide,
wherein the base rubber is a mixture of polybutadiene and a
styrene-butadiene rubber, the styrene-butadiene rubber having a
styrene bond content of not more than 35 wt %, and the
co-crosslinking agent is methacrylic acid; the core has a
deflection CH when compressed under a final load of 1,275 N (130
kgf) from an initial load of 98 N (10 kgf) of from 2.5 to 7.0 mm;
and the ball has formed on a surface thereof a plurality of
dimples, each having a spatial volume below a flat plane
circumscribed by an edge of the dimple, the sum of the individual
dimple spatial volumes, expressed as a percentage (VR) of the
volume of a hypothetical sphere were the ball to have no dimples on
the surface thereof, being from 0.95 to 1.7.
2. The solid golf ball of claim 1, wherein the metal oxide is zinc
oxide.
3. The solid golf ball of claim 1, wherein the polybutadiene
accounts for up to 80 wt % of the base rubber in the rubber
composition, the styrene-butadiene rubber accounts for between 20
and 80 wt % of the base rubber, and the isoprene rubber accounts
for between 0 and 60 wt % of the base rubber; and wherein the
rubber composition includes from 6 to 40 parts by weight of
methacrylic acid, from 6 to 30 parts by weight of the metal oxide,
from 0.3 to 5.0 parts by weight of the crosslinking initiator, and
from 0.1 to 1.0 part by weight of the antioxidant per 100 parts by
weight of the base rubber.
4. The solid golf ball of claim 1, wherein the core has a specific
gravity of from 1.05 to 1.2.
5. The solid golf ball of claim 1, wherein the cover is formed of a
resin material which is composed primarily of a polyurethane.
6. The solid golf ball of claim 5, wherein the resin material of
the cover is composed primarily of a thermoplastic
polyurethane.
7. The solid golf ball of claim 1, wherein the cover has a material
hardness, expressed in terms of Shore D hardness, of from 30 to
57.
8. The solid golf ball of claim 1, wherein the cover is formed of a
resin material having a breaking strength of from 20 to 80 MPa.
9. The solid golf ball of claim 1, wherein the cover is formed of a
resin material having an elongation of from 150 to 600%.
10. The solid golf ball of claim 1, wherein the cover has a
thickness of from 0.3 to 2.5 mm.
11. The solid golf ball of claim 1, wherein the ball has an initial
velocity (BV) of not more than 72 m/s.
12. The solid golf ball of claim 1, wherein the core has a
deflection CH (mm) when compressed under a final load of 1,275 N
(130 kgf) from an initial load of 98 N (10 kgf), the ball has, upon
initial measurement, a deflection BH1 (mm) when compressed under a
final load of 1,275 N (130 kgf) from an initial load of 98 N (10
kgf) and an initial velocity BV1 (m/s), and also has, when measured
again after 350 days of standing following initial measurement, a
deflection BH2 (mm) when compressed under a final load of 1,275 N
(130 kgf) from an initial load of 98 N (10 kgf) and an initial
velocity BV2 (m/s), such that: BH1 is from 2.5 to 7.0 mm, the ratio
CH/BH1 is from 0.95 to 1.1, the difference BH2-BH1 is not more than
0.2 mm, and the difference BV2-BV1 is not more than 0.3 m/s.
13. The solid golf ball of claim 1, wherein the dimples formed on
the surface of the ball satisfy conditions (1) to (6) below: (1)
the dimples have a peripheral edge provided with a roundness
represented by a radius of curvature R of from 0.5 to 2.5 mm; (2)
the ratio ER of a collective number of dimples RA having a radius
of curvature R to diameter D ratio (R/D) of at least 20%, divided
by a total number of dimples N on the surface of the ball, is from
15 to 95%; (3) the ball has thereon a plurality of dimple types of
differing diameter, and the ratio DER of a combined number of
dimples DE obtained by adding together dimples having an own
diameter and an own radius of curvature larger than or equal to a
radius of curvature of dimples of larger diameter than said own
diameter plus dimples of a type having a largest diameter, divided
by the total number of dimples N on the surface of the ball, is at
least 80%; (4) the number of dimple types of differing diameter is
3 or more; (5) the total number of dimples N is not more than 380;
and (6) the surface coverage SR of the dimples, which is the sum of
individual dimple surface areas, each defined by a flat plane
circumscribed by an edge of the dimple, expressed as a percentage
of the surface area of a hypothetical sphere were the ball to have
no dimples on the surface thereof, is from 60 to 74%.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of copending
application Ser. No. 13/351,790 filed on Jan. 17, 2012, the entire
contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a golf ball for long-term
use, and more specifically to a golf ball which has an excellent
durability to cracking and durability of appearance, which is able
to maintain a stable feel at impact and a stable flight performance
over an extended period of time, and which has a controlled
distance.
[0003] In order to maintain the durability of a golf ball in
long-term use, it is necessary to enhance the durability of each
member of the ball and the wear resistance of the outside surface.
It is also necessary to maintain the performance of the golf ball
in different seasons.
[0004] As is widely known, two-piece solid golf balls are composed
of a core and a cover, with the core being a crosslinked rubber
structure of certain desirable properties obtained by using a base
rubber composed primarily of cis-1,4-polybutadiene rubber to which
compounding ingredients such as a co-crosslinking agent, a metal
oxide and an organic peroxide have been added. For example, JP-A
59-49779 describes a rubber composition for the core of a two-piece
solid golf ball which is obtained by compounding a given amount of
zinc methacrylate as a co-crosslinking agent in
cis-1,4-polybutadiene rubber. However, when zinc methacrylate is
used in this way in a core-forming rubber composition, ensuring
good ball durability in long-term use has been difficult.
[0005] In addition, JP-A 2003-70936 describes a rubber composition
for the core of a two-piece solid golf ball which is obtained by
compounding a given amount of zinc acrylate in
cis-1,4-polybutadiene rubber. However, here too, when zinc acrylate
is used in the rubber-forming rubber composition, ensuring good
ball durability in long-term use has been difficult.
[0006] Also, JP-A 2004-180793 and JP-A 2008-149190 disclose golf
balls which use zinc acrylate in the core formulation and use a
thermoplastic polyurethane as the cover material. However,
drawbacks of such golf balls include a hard cover, a marked
decrease in ball flight following abrasion of the ball surface, and
poor durability of markings.
SUMMARY OF THE INVENTION
[0007] It is therefore an object of the present invention to
provide a solid golf ball which has an excellent durability to
cracking, durability of appearance and durability to ball surface
loss in long-term use, which maintains a stable feel at impact and
a stable flight performance over an extended period of time, and
which has a controlled distance.
[0008] As a result of extensive investigations, the inventors have
discovered that, in the fabrication of a solid golf ball having a
core and a cover, by using a mixture of polybutadiene and a
styrene-butadiene rubber as the base rubber and optimizing the
styrene bond content in the styrene-butadiene rubber, by using
methacrylic acid as a co-crosslinking agent and including a
specific amount of a crosslinking initiator per 100 parts by weight
of the base rubber, by optimizing the deflection of the core under
a specific load, the initial velocity of the finished ball, and the
dimple spatial occupancy VR, and by using a resin material having a
breaking strength of from 20 to 80 MPa and an elongation of from
150 to 600% as the cover material, owing to synergistic effects
from these constituent features, the resulting ball is endowed with
an excellent durability to cracking, durability to surface loss and
durability to abrasion that exceed the expectations of golf ball
designers. As a result, there can be obtained a golf ball which,
even in long-term use, maintains a good appearance, has a good feel
at impact and has a controlled distance.
[0009] That is, in the present invention, by including methacrylic
acid as a co-crosslinking agent in the core-forming rubber
composition, and by optimizing the amount of methacrylic acid and
the amount of crosslinking initiator, the durability to cracking
can be made much better than that in game balls. Moreover, having
the cover material composed primarily of polyurethane is desirable
in that it enables a golf ball of excellent durability to cracking
and durability to abrasion to be obtained. In addition, optimizing
the internal hardness profile of the core is desirable in that it
enables a solid golf ball having a good feel at impact to be
obtained.
[0010] Accordingly, the invention provides the following solid golf
ball.
[1] A solid golf ball comprising a core and a cover, the core being
formed of a rubber composition comprising a base rubber, a
co-crosslinking agent, a crosslinking initiator and a metal oxide,
wherein the base rubber is a mixture of polybutadiene and a
styrene-butadiene rubber, the styrene-butadiene rubber having a
styrene bond content of not more than 35 wt %, and the
co-crosslinking agent is methacrylic acid; the core has a
deflection CH when compressed under a final load of 1,275 N (130
kgf) from an initial load of 98 N (10 kgf) of from 2.5 to 7.0 mm;
and the ball has formed on a surface thereof a plurality of
dimples, each having a spatial volume below a flat plane
circumscribed by an edge of the dimple, the sum of the individual
dimple spatial volumes, expressed as a percentage (VR) of the
volume of a hypothetical sphere were the ball to have no dimples on
the surface thereof, being from 0.95 to 1.7. [2] The solid golf
ball of [1], wherein the metal oxide is zinc oxide. [3] The solid
golf ball of [1], wherein the polybutadiene accounts for up to 80
wt % of the base rubber in the rubber composition, the
styrene-butadiene rubber accounts for between 20 and 80 wt % of the
base rubber, and the isoprene rubber accounts for between 0 and 60
wt % of the base rubber; and wherein the rubber composition
includes from 6 to 40 parts by weight of methacrylic acid, from 6
to 30 parts by weight of the metal oxide, from 0.3 to 5.0 parts by
weight of the crosslinking initiator, and from 0.1 to 1.0 part by
weight of the antioxidant per 100 parts by weight of the base
rubber. [4] The solid golf ball of [1], wherein the core has a
specific gravity of from 1.05 to 1.2. [5] The solid golf ball of
[1], wherein the cover is formed of a resin material which is
composed primarily of a polyurethane. [6] The solid golf ball of
[5], wherein the resin material of the cover is composed primarily
of a thermoplastic polyurethane. [7] The solid golf ball of [1],
wherein the cover has a material hardness, expressed in terms of
Shore D hardness, of from 30 to 57. [8] The solid golf ball of [1],
wherein the cover is formed of a resin material having a breaking
strength of from 20 to 80 MPa. [9] The solid golf ball of [1],
wherein the cover is formed of a resin material having an
elongation of from 150 to 600%. [10] The solid golf ball of [1],
wherein the cover has a thickness of from 0.3 to 2.5 mm. [11] The
solid golf ball of [1], wherein the ball has an initial velocity
(BV) of not more than 72 m/s. [12] The solid golf ball of [1],
wherein the core has a deflection CH (mm) when compressed under a
final load of 1,275 N (130 kgf) from an initial load of 98 N (10
kgf), the ball has, upon initial measurement, a deflection BH1 (mm)
when compressed under a final load of 1,275 N (130 kgf) from an
initial load of 98 N (10 kgf) and an initial velocity BV1 (m/s),
and also has, when measured again after 350 days of standing
following initial measurement, a deflection BH2 (mm) when
compressed under a final load of 1,275 N (130 kgf) from an initial
load of 98 N (10 kgf) and an initial velocity BV2 (m/s), such that:
BH1 is from 2.5 to 7.0 mm, the ratio CH/BH1 is from 0.95 to 1.1,
the difference BH2-BH1 is not more than 0.2 mm, and the difference
BV2-BV1 is not more than 0.3 m/s. [13] The solid golf ball of [1],
wherein the dimples formed on the surface of the ball satisfy
conditions (1) to (6) below:
[0011] (1) the dimples have a peripheral edge provided with a
roundness represented by a radius of curvature R of from 0.5 to 2.5
mm;
[0012] (2) the ratio ER of a collective number of dimples RA having
a radius of curvature R to diameter D ratio (R/D) of at least 20%,
divided by a total number of dimples N on the surface of the ball,
is from 15 to 95%;
[0013] (3) the ball has thereon a plurality of dimple types of
differing diameter, and the ratio DER of a combined number of
dimples DE obtained by adding together dimples having an own
diameter and an own radius of curvature larger than or equal to a
radius of curvature of dimples of larger diameter than said own
diameter plus dimples of a type having a largest diameter, divided
by the total number of dimples N on the surface of the ball, is at
least 80%;
[0014] (4) the number of dimple types of differing diameter is 3 or
more;
[0015] (5) the total number of dimples N is not more than 380;
and
[0016] (6) the surface coverage SR of the dimples, which is the sum
of individual dimple surface areas, each defined by a flat plane
circumscribed by an edge of the dimple, expressed as a percentage
of the surface area of a hypothetical sphere were the ball to have
no dimples on the surface thereof, is from 60 to 74%.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0017] FIG. 1 is a schematic cross-sectional diagram of a solid
golf ball according to one embodiment of the invention.
[0018] FIG. 2 is a schematic diagram of a core illustrating
positions A to F in a core hardness profile.
[0019] FIG. 3 is a schematic diagram showing an example of a dimple
cross-section.
[0020] FIG. 4A is a top view and FIG. 4B is a side view showing an
example of a dimple configuration.
[0021] FIG. 5 is a top view showing the markings that were placed
on the golf balls fabricated in the examples and the comparative
examples.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The invention is described more fully below.
[0023] The solid golf ball of the invention has a structure which
is exemplified by, as shown in FIG. 1, a two-piece solid golf ball
G 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.
[0024] The core is obtained by vulcanizing a rubber composition
composed primarily of a rubber material. The rubber composition
used to form the core includes a base rubber, a co-crosslinking
agent, a crosslinking initiator, a metal oxide, an antioxidant and,
optionally, an inert filler. In the invention, a mixture of
polybutadiene with a styrene-butadiene rubber is used as the base
rubber. Also, in the present invention, as will be subsequently
described, it is preferable for the core cross-sectional hardness
to change in specific ways from the surface to the center of the
core, and for the core cross-sectional hardness profile to be
adjusted within certain desired ranges. To this end, in formulating
the core, it is essential to suitably adjust, for example, the
amounts in which the various subsequently described compounding
ingredients are included, the vulcanization temperature and the
vulcanization time.
[0025] The polybutadiene used as a rubber component must have a
cis-1,4 bond content of at least 60 wt %, preferably at least 80 wt
%, more preferably at least 90 wt %, and most preferably at least
95 wt %. If the cis-1,4 bond content is too low, the rebound may
decrease. In addition, the polybutadiene has a 1,2-vinyl bond
content of preferably 2 wt % or less, more preferably 1.7 wt % or
less, and even more preferably 1.5 wt % or less.
[0026] The polybutadiene has a Mooney viscosity (ML.sub.1+4
(100.degree. C.)) which is preferably at least 30, more preferably
at least 35, and even more preferably at least 40. The upper limit
is preferably not more than 100, more preferably not more than 80,
even more preferably not more than 70, and most preferably not more
than 60.
[0027] The term "Mooney viscosity" used herein refers to an
industrial indicator of viscosity (JIS K6300) as measured with a
Mooney viscometer, which is a type of rotary plastometer. This
value is represented by the unit symbol ML.sub.1+4 (100.degree.
C.), wherein "M" stands for Mooney viscosity, "L" stands for large
rotor (L-type), and "1+4" stands for a pre-heating time of 1 minute
and a rotor rotation time of 4 minutes. The "100.degree. C."
indicates that measurement was carried out at a temperature of
100.degree. C.
[0028] In order to obtain the rubber composition in a molded and
vulcanized form which has a good rebound, it is preferable for the
polybutadiene to have been synthesized using a rare-earth catalyst
or a Group VIII metal compound catalyst.
[0029] The rare-earth catalyst is not subject to any particular
limitation, although preferred use may be made of a catalyst which
employs a lanthanum series rare-earth compound. Also, where
necessary, an organoaluminum compound, an alumoxane, a
halogen-bearing compound and a Lewis base may be used in
combination with the lanthanum series rare-earth compound.
Preferred use can be made of, as the various above compounds, those
compounds mentioned in JP-A 11-35633, JP-A 11-164912 and JP-A
2002-293996.
[0030] Of the above rare-earth catalysts, the use of a neodymium
catalyst that employs a neodymium compound, which is a lanthanide
series rare-earth compound, is especially recommended. In such a
case, a polybutadiene rubber having a high cis-1,4 bond content and
a low 1,2-vinyl bond content can be obtained at an excellent
polymerization activity.
[0031] The polybutadiene has a molecular-weight distribution Mw/Mn
(Mw being the weight-average molecular weight, and Mn being the
number-average molecular weight) of preferably at least 1.0, more
preferably at least 2.0, even more preferably at least 2.2, and
most preferably at least 2.4. The upper limit is preferably 6.0 or
less, more preferably 5.0 or less, and even more preferably 4.5 or
less. If Mw/Mn is too low, the workability may decrease. On the
other hand, if Mw/Mn is too high, the rebound may decrease.
[0032] The above polybutadiene used in the base rubber accounts for
a proportion of the overall base rubber which, although not subject
to any particular limitation, is preferably not more than 80 wt %,
more preferably not more than 70 wt %, even more preferably not
more than 60 wt %, and most preferably not more than 57 wt %. The
lower limit is preferably at least 30 wt %, more preferably at
least 35 wt %, and even more preferably at least 38 wt %.
[0033] Illustrative examples of cis-1,4-polybutadiene rubbers which
may be used include the high-cis products BR01, BR11, BR02, BR02L,
BR02LL, BR730 and BR51, all of which are available from JSR
Corporation.
[0034] In the present invention, a styrene-butadiene rubber (SBR)
is used together with the above polybutadiene rubber (BR) as the
base rubber. The styrene-butadiene rubber is described below.
[0035] A solution-polymerized styrene-butadiene rubber or an
emulsion-polymerized styrene-butadiene rubber may be used as the
styrene-butadiene rubber (SBR). For example, use may be made of the
solution-polymerized products SBR-SL552, SBR-SL555 and SBR-SL563
(available from JSR Corporation) as the solution-polymerized
styrene-butadiene rubber, and use may be made of the
emulsion-polymerized products SBR 1500, SBR 1502 and SBR 1507
(available from JSR Corporation) as the emulsion-polymerized
styrene-butadiene rubber.
[0036] The styrene bond content in the styrene-butadiene rubber is
preferably at least 5 wt %, more preferably at least 10 wt %, even
more preferably at least 15 wt %, and most preferably at least 18
wt %. The upper limit is preferably not more than 35 wt %, more
preferably not more than 30 wt %, even more preferably not more
than 25 wt %, and most preferably not more than 22 wt %. If the
styrene bond content is too high, due to temperature changes on
account of seasonal differences, the core will become harder and
large changes will occur in the rebound. On the other hand, if the
styrene bond content is too low, the ease of operation during
surface grinding of the core will dramatically decrease. Also, if
the styrene bond content is too high, the scuff resistance at low
temperature may worsen.
[0037] The styrene-butadiene rubber accounts for a proportion of
the overall base rubber which is preferably at least 20 wt %, more
preferably at least 25 wt %, even more preferably at least 30 wt %,
and most preferably at least 35 wt %. The upper limit is preferably
not more than 80 wt %, more preferably not more than 70 wt %, even
more preferably not more than 60 wt %, and most preferably not more
than 57 wt %.
[0038] Rubber ingredients other than the above polybutadiene and
styrene-butadiene rubber (SBR) may also be included in the base
rubber, insofar as the objects of the invention are attainable.
Illustrative examples of rubber ingredients other than the above
polybutadiene and styrene-butadiene rubber (SBR) include
polybutadienes other than the above polybutadiene, and other diene
rubbers such as natural rubbers, isoprene rubbers (IR) and
ethylene-propylene-diene rubbers.
[0039] Isoprene rubbers (IR) which may be used include those having
a cis-1,4 bond content of at least 60 wt %, preferably at least 80
wt %, and more preferably at least 90 wt %, and having a Mooney
viscosity (ML.sub.1+4 (100.degree. C.)) of at least 60, preferably
at least 70, and more preferably at least 80, with an upper limit
of not more than 90, and preferably not more than 85. For example,
the product IR2200 available from JSR Corporation may be used. The
proportion of the overall base rubber represented by rubber
ingredients other than polybutadiene is preferably more than 0 wt
%, more preferably at least 2 wt %, and most preferably at least 5
wt %. The upper limit is preferably not more than 60 wt %, more
preferably not more than 40 wt %, even more preferably not more
than 20 wt %, and most preferably not more than 10 wt %.
[0040] In the invention, methacrylic acid is an essential
ingredient which is used as the co-crosslinking agent. Methacrylic
acid is included in an amount, per 100 parts by weight of the base
rubber, of preferably at least 6 parts by weight, more preferably
at least 8 parts by weight, even more preferably at least 10 parts
by weight, and most preferably at least 11.5 parts by weight. The
upper limit in the amount of methacrylic acid is preferably not
more than 40 parts by weight, more preferably not more than 35
parts by weight, even more preferably not more than 30 parts by
weight, and most preferably not more than 25 parts by weight.
Including too much co-crosslinking agent may make the core too
hard, giving the ball an unpleasant feel at impact. On the other
hand, including too little co-crosslinking agent may make the core
too soft, also giving the ball an unpleasant feel at impact.
[0041] It is preferable to use an organic peroxide as the
crosslinking initiator. Examples of commercial products that may be
advantageously used include Percumyl D (from NOF Corporation),
Perhexa C40 (NOF Corporation) and Trigonox 29-40b (Akzo Nobel
N.V.). These may be used singly or as a combination of two or more
thereof.
[0042] The amount of crosslinking initiator per 100 parts by weight
of the base rubber may be set to preferably at least 0.3 part by
weight, more preferably at least 0.5 part by weight, and even more
preferably at least 0.7 part by weight. The upper limit in the
amount of crosslinking initiator may be set to preferably not more
than 5.0 parts by weight, more preferably not more than 4.0 parts
by weight, even more preferably not more than 3.0 parts by weight,
and most preferably not more than 2.0 parts by weight. Including
too much crosslinking initiator may make the core too hard, giving
the ball an unpleasant feel at impact and also substantially
lowering the durability to cracking. On the other hand, including
too little crosslinking initiator may make the core too soft,
giving the ball an unpleasant feel at impact and also substantially
lowering productivity.
[0043] Although not subject to any particular limitation, in this
invention, the use of zinc oxide as the metal oxide is preferred.
The use of metal oxides other than zinc oxide is also possible,
insofar as the objects of the invention are attainable. The metal
oxide is included in an amount, per 100 parts by weight of the base
rubber, of preferably at least 6 parts by weight, more preferably
at least 8 parts by weight, even more preferably at least 10 parts
by weight, and most preferably at least 12 parts by weight. The
upper limit in the amount of metal oxide is preferably not more
than 30 parts by weight, more preferably not more than 28 parts by
weight, even more preferably not more than 26 parts by weight, and
most preferably not more than 24 parts by weight. Including too
much or too little metal oxide may make it impossible to obtain a
suitable weight and a good hardness and rebound.
[0044] In the practice of the invention, it is preferable to
include an antioxidant in the rubber composition. For example, use
may be made of the commercial products Nocrac NS-6, Nocrac NS-30
and Nocrac 200 (all available from Ouchi Shinko Chemical Industry
Co., Ltd.). These may be used singly or as combinations of two or
more thereof.
[0045] The amount of antioxidant included per 100 parts by weight
of the base rubber, although not subject to any particular
limitation, is preferably at least 0.1 part by weight, and more
preferably at least 0.15 part by weight, but is preferably not more
than 1.0 part by weight, more preferably not more than 0.7 part by
weight, and even more preferably not more than 0.4 part by weight.
Including too much or too little antioxidant may make it impossible
to achieve a suitable core hardness gradient, as a result of which
a good rebound, good durability and good spin rate-lowering effect
on full shots may not be achieved.
[0046] Preferred use may be made of, for example, barium sulfate,
calcium carbonate or silica as the inert filler. Any one of these
may be used alone or two or more may be used in combination. The
amount of inert filler included is not particularly limited,
although this amount is preferably more than 0, and may be set to
preferably at least 1 part by weight, and more preferably at least
5 parts by weight, per 100 parts by weight of the base rubber. The
upper limit in the amount of inert filler included may be set to
preferably not more than 50 parts by weight, more preferably not
more than 40 parts by weight, and even more preferably not more
than 30 parts by weight. If the amount of inert filler included is
too large or too small, a suitable weight and a good hardness and
rebound may not be achieved.
[0047] In the practice of the invention, from a resource recycling
standpoint, one or more type of powder selected from among specific
rubber powders (I-a) and (I-b) and a polyurethane resin powder (II)
may be included in the rubber ingredients of the core. In this
case, such a ground powder or abraded powder may be included in an
amount, per 100 parts by weight of the base rubber, which is more
than 0, preferably at least 2 wt %, and most preferably at least
about 5 wt %. The upper limit is preferably not more than about 40
wt %, more preferably not more than about 35 wt %, even more
preferably not more than about 30 wt %, and most preferably not
more than about 25 wt %. The rubber powders (I) and the
polyurethane resin powder (II) used in the invention may be
obtained by Method (i) or Method (ii) below.
Method (i)
[0048] Materials obtained by finely grinding, in cases where golf
ball covers are formed of a polyurethane resin, the resin from
runners discharged as waste during the molding of such golf ball
covers as well as flash generated during molding, defectively
molded cores, and also the powder obtained when golf balls and golf
ball cores are surface ground, can be advantageously used as the
specific rubber powders (I-a) and (I-b) and the polyurethane resin
powder (II).
Method (ii)
[0049] Use can be made of materials obtained by employing a
granulator to finely grind defective moldings and golf balls which
have been used and discarded, screening the finely ground material,
and thereby collecting the specific rubber powders (I-a) and (I-b)
and the polyurethane resin powder (II) having particle sizes at or
below a given size. When golf balls are granulated, the resulting
material may be contaminated with impurities such as paint and ink.
However, this material may be directly incorporated into the rubber
composition if the amount of such contamination is not large.
[0050] The particle sizes of the above rubber powders (I-a) and
(I-b) and the polyurethane resin powder (II), expressed as the size
of the screen openings, must be set to not more than 3 mm, and may
be set to preferably 2 mm or less, more preferably 1.5 mm or less,
and even more preferably 1 mm or less. If the particle sizes of the
rubber powders (I-a) and (I-b) and the polyurethane resin powder
(II) exceed the above-indicated size, the durability of the golf
ball may be adversely affected, in addition to which it may not be
possible to fully ensure adhesion due to an anchoring effect.
[0051] The polyurethane resin powder (II) may be either a
thermoplastic polyurethane or a thermoset polyurethane resin,
although the use of a thermoplastic polyurethane is more
preferred.
[0052] The present invention, by including in the core material one
or more powder selected from among the two specific rubber powders
(I-a) and (I-b) and the polyurethane resin powder (II), confers a
suitable surface roughness to the core, thereby making it possible
to increase the surface area of contact with the adjoining cover
and improve adhesion due to an anchoring effect. In particular, by
using a thermoplastic polyurethane in the cover material, the
polyurethane resins included in the cover material and the core
material melt during molding of the cover material, enabling
adhesion between the core and the cover to be increased even
further.
Rubber Powder (I-a)
[0053] In the invention, the rubber powder (I-a) includes, as an
essential ingredient, methacrylic acid or a metal salt thereof. By
using (I-a) a rubber powder containing methacrylic acid (MAA) or a
metal salt thereof, it is possible to enhance in particular the
durability of the golf ball. That is, a material obtained by
granulating the above-described core material can be advantageously
used as the rubber powder (I-a), in which case the rubber material
that is granulated will include methacrylic acid (MAA) or a metal
salt thereof as the unsaturated carboxylic acid or a metal salt
thereof. The amount of the methacrylic acid or a metal salt thereof
which is included in the foregoing rubber powder (I-a) may be set
to preferably at least 5 wt %, more preferably at least 10 wt %,
and even more preferably at least 15 wt %. The upper limit may be
set to preferably not more than 60 wt %, more preferably not more
than 50 wt %, even more preferably not more than 40 wt %, and most
preferably not more than 30 wt %. If the content is too small, the
durability may worsen, and if the content is too large, the rebound
may decrease.
Rubber Powder (I-b)
[0054] In the invention, the rubber powder (I-b) includes, as an
essential ingredient, acrylic acid (AA) or a metal salt of acrylic
acid. By using a rubber powder (I-b) containing acrylic acid (AA)
or a metal salt of acrylic acid, a good golf ball durability is
maintained, in addition to which the initial velocity of the ball
is increased, enabling the distance traveled by the ball to be
enhanced. That is, a material obtained by granulating the
above-described core material can be advantageously used as the
rubber powder (I-b), in which case acrylic acid (AA) or a metal
salt thereof is included as an unsaturated carboxylic acid or a
metal salt thereof in the rubber material that is granulated.
Examples of metal salts of acrylic acid include zinc acrylate
(ZDA), magnesium acrylate, sodium acrylate, potassium acrylate,
aluminum acrylate and calcium acrylate. The content of the acrylic
acid or a metal salt thereof which is included in the rubber powder
(I-b) may be set to preferably at least 3 wt %, more preferably at
least 10 wt %, and even more preferably at least 15 wt %. The upper
limit may be set to preferably not more than 60 wt %, more
preferably not more than 50 wt %, even more preferably not more
than 40 wt %, and most preferably not more than 30 wt %. If the
content is too low, the durability may be inferior, and if the
content is too high, the rebound may decrease.
Polyurethane Resin Powder (II)
[0055] When use is made of the above-described thermoplastic
polyurethane powder, it is preferable to use such a powder having a
flow starting point of at least 150.degree. C. The flow starting
point is more preferably at least 160.degree. C., and even more
preferably at least 170.degree. C. The upper limit is preferably
not more than 320.degree. C., more preferably not more than
300.degree. C., and even more preferably not more than 280.degree.
C. If the flow starting point is too low, the powder will end up
melting at the time of core vulcanization, which may result in a
loss of core durability and symmetry. On the other hand, if the
flow starting point of the powder is too high, it will not be
possible to melt the polyurethane at the surface during molding of
the cover, as a result of which an additional durability improving
effect arising from the use of a thermoplastic polyurethane may not
be attainable.
[0056] The core may be produced by using a known method to
vulcanize and cure a rubber composition containing the various
above ingredients. For example, production may be carried out by
using a mixing apparatus such as a Banbury mixer or a roll mill to
mix the rubber composition, compression molding or injection
molding the mixed composition in a core mold, then heating and
curing the molded body at a temperature sufficient for the organic
peroxide and co-crosslinking agent to act, thereby giving a core
having a specific hardness profile. Although the vulcanization
conditions are not subject to any particular limitation, the
vulcanization temperature is generally from about 100.degree. C. to
about 200.degree. C., with the lower limit being preferably at
least 150.degree. C., and more preferably at least 155.degree. C.,
and the upper limit being preferably not more than 180.degree. C.,
more preferably not more than 175.degree. C., and most preferably
not more than 170.degree. C. The vulcanization time is generally in
a range of about 10 to about 40 minutes, with the lower limit being
preferably at least 12 minutes and the upper limit being preferably
not more than 30 minutes, more preferably not more than 25 minutes,
and most preferably not more than 20 minutes. The core hardness
profile in the invention is achievable through a combination of the
vulcanization conditions with preparation of the rubber
formulation.
[0057] The core diameter, although not subject to any particular
limitation, is typically at least 38.0 mm, preferably at least 38.9
mm, and more preferably at least 39.3 mm. The upper limit is
preferably not more than 42.1 mm, and more preferably not more than
41.1 mm. At a core diameter outside of this range, the durability
of the ball to cracking may worsen dramatically or the initial
velocity of the ball may decrease.
[0058] It is recommended that the core have a specific gravity of
at least 1.05, preferably at least 1.08, and more preferably at
least 1.1, but not more than 1.2, preferably not more than 1.15,
and more preferably not more than 1.13.
[0059] The core deflection (CH) under loading, i.e., the deflection
by the core when compressed under a final load of 1,275 N (130 kgf)
from an initial load of 98 N (10 kgf), is at least 2.5 mm,
preferably at least 2.6 mm, and more preferably at least 2.7 mm.
The upper limit in the core deflection is not more than 7.0 mm,
preferably not more than 6.0 mm, more preferably not more than 5.5
mm, and most preferably not more than 5.2 mm. If the core
deflection (CH) is too small, the feel of the golf ball at impact
may be so hard as to make the ball unpleasant to use. On the other
hand, if the core deflection is too large, the feel of the golf
ball at impact may be so soft as to make the ball unpleasant to
use, in addition to which the productivity may decline
considerably.
[0060] The core rebound (CV) is typically at least 60 m/s,
preferably at least 63 m/s, more preferably at least 66 m/s, and
most preferably at least 67 m/s. The upper limit is preferably not
more than 73 m/s, more preferably not more than 72.5 m/s, and even
more preferably not more than 72 m/s. At a core rebound outside of
this range, the distance of the ball may dramatically decline or
the ball may travel too far, making proper control of the ball
impossible. As used herein, "core rebound" is synonymous with core
initial velocity.
[0061] In the present invention, as shown in the schematic diagram
of the core in FIG. 2, letting A be the JIS-C hardness at the
surface of the core, B be the JIS-C hardness at a position 2 mm
inside the core surface, C be the JIS-C hardness at a position 5 mm
inside the core surface, D be the JIS-C hardness at a position 10
mm inside the core surface, E be the JIS-C hardness at a position
15 mm inside the core surface, and F be the JIS-C hardness at the
center of the core, it is preferable for the respective values A to
F to fall within the specific ranges indicated below. By thus
setting the hardness profile at the core interior within specific
ranges, both a comfortable feel at impact close to that of a game
ball and a good durability to cracking can be obtained.
[0062] Letting A be the JIS-C hardness at the surface of the core,
the value of A is preferably at least 60, more preferably at least
63, and even more preferably at least 65. The upper limit is
preferably not more than 88, more preferably not more than 86, and
even more preferably not more than 84.
[0063] Letting B be the JIS-C hardness at a position 2 mm inside
the core surface, the value of B is preferably at least 54, more
preferably at least 57, and even more preferably at least 59. The
upper limit is preferably not more than 83, more preferably not
more than 81, and even more preferably not more than 79.
[0064] Letting C be the JIS-C hardness at a position 5 mm inside
the core surface, the value of C is preferably at least 56, more
preferably at least 59, and even more preferably at least 61. The
upper limit is preferably not more than 85, more preferably not
more than 83, and even more preferably not more than 81.
[0065] Letting D be the JIS-C hardness at a position 10 mm inside
the core surface, the value of D is preferably at least 54, more
preferably at least 57, and even more preferably at least 60. The
upper limit is preferably not more than 80, more preferably not
more than 78, and even more preferably not more than 76.
[0066] Letting E be the JIS-C hardness at a position 15 mm inside
the core surface, the value of E is preferably at least 51, more
preferably at least 54, and even more preferably at least 57. The
upper limit is preferably not more than 75, more preferably not
more than 73, even more preferably not more than 71, and most
preferably not more than 70.
[0067] Letting F be the JIS-C hardness at the center of the core,
the value of F is preferably at least 48, more preferably at least
51, and even more preferably at least 54. The upper limit is
preferably not more than 72, more preferably not more than 70, and
even more preferably not more than 68.
[0068] Moreover, it is preferable for the hardness profile of the
core to satisfy the hardness relationship
A>B<C.gtoreq.D>E>F, for the value A-F to be not more
than 19, for the core to be formed in such a way that A has the
highest hardness among A to F, and for the value A-C to be from 0
to 8. If the above conditions are not satisfied, the ball may have
a diminished feel at impact and a reduced durability to
cracking.
[0069] The value of A-C is typically from 0 to 8. The lower limit
for this value is preferably greater than 0, more preferably at
least 1, and even more preferably at least 2. The upper limit is
preferably not more than 8, more preferably not more than 6, and
even more preferably not more than 4. The value of A-F has a lower
limit of preferably at least 2, more preferably at least 4, and
even more preferably at least 6. The upper limit in this value is
preferably not more than 19, more preferably not more than 18, and
even more preferably not more than 17.
[0070] In the practice of the invention, the core may be subjected
to surface treatment with a solution containing a haloisocyanuric
acid and/or a metal salt thereof.
[0071] Prior to surface-treating the core with a solution
containing a haloisocyanuric acid and/or a metal salt thereof,
adhesion between the core surface and the adjoining cover material
can be further enhanced by subjecting the surface of the core to
grinding treatment ("surface grinding").
[0072] Such grinding treatment removes the skin layer from the
surface of the vulcanized core, and thus makes it possible to both
enhance the ability of the solution of haloisocyanuric acid and/or
a metal salt thereof to penetrate the core surface and also to
increase the surface area of contact with the adjoining cover
material. Exemplary surface grinding methods include buffing,
barrel grinding and centerless grinding.
[0073] The haloisocyanuric acid and metal salts thereof are
compounds of the following formula (I).
##STR00001##
In the formula, X is a hydrogen atom, a halogen atom or an alkali
metal atom. At least one occurrence of X is a halogen atom.
Preferred halogen atoms include fluorine, chlorine and bromine,
with chlorine being especially preferred. Preferred alkali metal
atoms include lithium, sodium and potassium.
[0074] Illustrative examples of the haloisocyanuric acid and/or a
metal salt thereof include chloroisocyanuric acid, sodium
chloroisocyanurate, potassium chloroisocyanurate,
dichloroisocyanuric acid, sodium dichloroisocyanurate, sodium
dichloroisocyanurate dihydrate, potassium dichloroisocyanurate,
trichloroisocyanuric acid, tribromoisocyanuric acid,
dibromoisocyanuric acid, bromoisocyanuric acid, sodium and other
salts of dibromisocyanuric acid, as well as hydrates thereof, and
difluoroisocyanuric acid. Of these, chloroisocyanuric acid, sodium
chloroisocyanurate, potassium chloroisocyanurate,
dichloroisocyanuric acid, sodium dichloroisocyanurate, potassium
dichloroisocyanurate and trichloroisocyanuric acid are preferred
because they are readily hydrolyzed by water to form acid and
chlorine, and thus play the role of initiating addition reactions
to the double bonds on the diene rubber molecules. The use of
trichloroisocyanuric acid provides an especially outstanding
adhesion-improving effect.
[0075] The haloisocyanuric acid and/or a metal salt thereof is
preferably dissolved in water or an organic solvent and used as a
solution.
[0076] When water is used as the solvent, the content of the
haloisocyanuric acid and/or a metal salt thereof in the treatment
solution, although not subject to any particular limitation, may be
set to preferably at least 0.5 part by weight, more preferably at
least 1 part by weight, and even more preferably at least 3 parts
by weight, per 100 parts by weight of water. If the content of
haloisocyanuric acid and/or a metal salt thereof is too low, the
adhesion improving effect expected after core surface treatment may
not be obtained and the durability to impact may be poor. The upper
limit is the saturated solution concentration. However, from the
standpoint of cost effectiveness, it is preferable to set the upper
limit to about 10 parts by weight per 100 parts by weight of water.
The core is immersed in the treatment solution for a length of time
which, although not subject to any particular limitation, may be
set to preferably at least 0.3 second, more preferably at least 3
seconds, and even more preferably at least 10 seconds. The upper
limit is preferably not more than 5 minutes, and more preferably
not more than 4 minutes. If the immersion time is too short, the
anticipated treatment effects may not be obtained, whereas if the
immersion time is too long, a loss in productivity may occur.
[0077] In cases where use is made of an organic solvent, the
solvent may be a known organic solvent, with the use of an organic
solvent that is soluble in water being especially preferred.
Examples include ethyl acetate, acetone and methyl ethyl ketone. Of
these, acetone is especially preferred on account of its ability to
penetrate the core surface. The use of a water-soluble solvent is
preferred for a number of reasons. For example, such solvents
readily take up moisture, the moisture which has been taken up
readily undergoing a hydrolysis reaction with the haloisocyanuric
acid and/or a metal salt thereof adhering to the core surface.
Another reason is that, when water washing is used in a subsequent
step, the affinity of water to the core surface increases, along
with which a hydrolysis reaction between the water and the
haloisocyanuric acid and/or a metal salt thereof more readily
arises.
[0078] When dissolved in an organic solvent, the content of the
haloisocyanuric acid and/or a metal salt thereof in the solution is
preferably at least 0.3 wt %, more preferably at least 1 wt %, and
even more preferably at least 2.5 wt %. At less than 0.3 wt %, the
adhesion improving effect anticipated following core surface
treatment may not obtained, which may result in a poor durability
to impact. The upper limit in the content may be as high as the
saturated solution concentration. However, from the standpoint of
cost effectiveness, when prepared as an acetone solution, for
example, setting the upper limit in content to about 10 wt % is
preferred. The core is immersed in the solution for a length of
time which, although not subject to any particular limitation, is
preferably at least 0.3 second, more preferably at least 3 seconds,
and even more preferably at least 10 seconds. The upper limit is
preferably not more than 5 minutes, and more preferably not more
than 4 minutes. If the immersion time is too short, the desired
effects of treatment may not be obtained, whereas if the immersion
time is too long, a loss in productivity may occur.
[0079] The method of treating the core surface with a
haloisocyanuric acid and/or a metal salt thereof is exemplified by
methods which involve coating the core surface with a solution of
haloisocyanuric acid and/or a metal salt thereof by brushing or
spraying on the solution, and methods in which the core is immersed
in a solution of the haloisocyanuric acid and/or a metal salt
thereof. From the standpoint of productivity and high penetrability
of the core surface by the solution, the use of an immersion method
is especially preferred.
[0080] After the core has been surface treated with a solution
containing haloisocyanuric acid and/or a metal salt thereof, it is
preferable to wash the surface of the core with water. Water
washing of the core surface may be carried out by a method such as
running water, spraying, or soaking in a washing tank. However,
because the aim here is not merely to wash, but also to initiate
and promote the desired treatment reactions, the washing method
should be one that is not too vigorous. Accordingly, preferred use
may be made of washing by soaking in a washing tank. In such a
case, it is desirable to place the cores to be washed from about
one to five times in a washing tank that has been filled with fresh
water.
[0081] Treating the core surface with a haloisocyanuric acid and/or
a metal salt thereof greatly improves adhesion between the core
surface and the cover. The reason for this is not well understood,
but is thought to be as follows.
[0082] First, the haloisocyanuric acid and/or a metal salt thereof,
together with the solvent, penetrates to the interior of the diene
rubber making up the core and approaches the vicinity of the double
bonds on the diene rubber backbone. Water then enters the core
surface, whereupon the haloisocyanuric acid and/or a metal salt
thereof is hydrolyzed by the water, releasing the halogen. The
halogen attacks a double bond on the diene rubber backbone located
nearby, as a result of which an addition reaction proceeds. In the
course of this addition reaction, the liberated isocyanuric acid is
added, together with the halogen, to the diene rubber backbone
while retaining its cyclic structure. The added isocyanuric acid
has three --NHCO-- structures on the molecule.
[0083] Because --NHCO-- structures are thereby conferred to the
core surface that has been treated with the haloisocyanuric acid
and/or a metal salt thereof, adhesion with the cover material
improves further. It is most likely because of this that the
durability of the golf ball to impact improves. Moreover, when a
polyurethane elastomer or polyamide elastomer having the same
--NHCO-- structures on the polymer molecules is used as the cover
material, the affinity increases even further, presumably
increasing the durability to impact.
[0084] Following surface treatment, when the material at the
surface portion of the solid core is examined by differential
scanning calorimetry (DSC), no exothermic or endothermic peaks are
observed from room temperature to 300.degree. C. This means that
the functional groups which have been introduced maintain a stable
state within this temperature range. In other words, during molding
of the cover material, the functional groups which have been
introduced do not undergo degradation or the like due to heat, and
thus continue to be effective. Also, because melting in the manner
of a hot melt resin does not arise, deleterious effects on
durability and quality of appearance, such as resin bleed out to
the parting line, do not occur. In addition, the very fact that the
material in the surface portion of the solid core following the
surface treatment described above is stable may be regarded as
evidence that the isocyanuric acid having a melting point above
300.degree. C. has been added with its molecular structure still
intact.
[0085] In cases where, using an organic solvent, the addition of
isocyanuric acid and chlorine to the surface of diene rubber has
occurred, changes in the bonding states before and after addition
appear in an infrared absorption spectrum as increases in the
C.dbd.O bond (stretching) absorption peak at 1725 to 1705
cm.sup.-1, the broad N--H bond (stretching) absorption peak at 3450
to 3300 cm.sup.-1, and the C--Cl bond absorption peak at 800 to 600
cm.sup.-1. Hence, by measuring the IR absorption spectrum of a
surface-treated core and confirming increases in these absorption
peaks, it is possible to qualitatively confirm that isocyanuric
acid and chlorine addition to diene rubber molecules at the core
surface has indeed occurred.
[0086] Next, the material making up the cover which directly
encases the core is described.
[0087] In this invention, a thermoplastic resin such as an ionomer
resin or polyurethane may be used as the resin component of the
cover. In particular, the use of a resin material composed
primarily of polyurethane is preferred. Specifically, use may be
made of a thermoplastic polyurethane elastomer or a thermoset
polyurethane resin, with the use of a thermoplastic polyurethane
elastomer being especially preferred.
[0088] The thermoplastic polyurethane elastomer has a structure
composed of soft segments formed from a polymeric polyol (polymeric
glycol) and hard segments formed from a chain extender and a
diisocyanate. Here, the polymeric polyol serving as a starting
material may be any which has hitherto been used in the art
relating to thermoplastic polyurethane materials, and is not
subject to any particular limitation. Exemplary polymeric polyols
include polyester polyols and polyether polyols. Polyether polyols
are more preferable than polyester polyols because they enable
thermoplastic polyurethane materials having a high rebound
resilience and excellent low-temperature properties to be
synthesized. Illustrative examples of polyether polyols include
polytetramethylene glycol and polypropylene glycol.
Polytetramethylene glycol is especially preferred from the
standpoint of the rebound resilience and the low-temperature
properties. The polymeric polyol has an average molecular weight of
preferably between 1,000 and 5,000. To synthesize a thermoplastic
polyurethane material having a high rebound resilience, an average
molecular weight of between 2,000 and 4,000 is especially
preferred.
[0089] The chain extender employed is preferably one which has
hitherto been used in the art relating to thermoplastic
polyurethane materials. Illustrative examples include, but are not
limited to, 1,4-butylene glycol, 1,2-ethylene glycol,
1,3-butanediol, 1,6-hexanediol and 2,2-dimethyl-1,3-propanediol.
The average molecular weight of these chain extenders is preferably
between 20 and 15,000.
[0090] The diisocyanate employed is preferably one which has
hitherto been used in the art relating to thermoplastic
polyurethane materials. Illustrative examples include, but are not
limited to, aromatic diisocyanates such as 4,4'-diphenylmethane
diisocyanate, 2,4-toluene diisocyanate and 2,6-toluene
diisocyanate, and aliphatic diisocyanates such as hexamethylene
diisocyanate. Depending on the type of isocyanate, control of the
crosslinking reaction during injection molding may be difficult. In
this invention, the use of 4,4'-diphenylmethane diisocyanate, which
is an aromatic diisocyanate, is most preferred.
[0091] A commercial product may be advantageously used as the
thermoplastic polyurethane material composed of the above
materials. Illustrative examples include those available under the
trade names Pandex T8180, Pandex T8195, Pandex T8290, Pandex T8295
and Pandex T8260 (all available from DIC Bayer Polymer, Ltd.), and
those available under the trade names Resamine 2593 and Resamine
2597 (available from Dainichiseika Color & Chemicals Mfg. Co.,
Ltd.).
[0092] The above polyurethane, although not subject to any
particular limitation, is preferably a material which is capable of
melt-bonding with the above-described polyurethane resin powder
(II); a material which, like the polyurethane resin powder (II), is
a thermoplastic resin is preferred because melt bonding can be
expected to occur. The use of a polyurethane having a high
isocyanate content is especially preferred, and makes it possible
to improve adhesion with the core material.
[0093] The cover has a thickness which is preferably at least 0.3
mm, more preferably at least 0.5 mm, and even more preferably at
least 0.7 mm. The upper limit is preferably not more than 2.5 mm,
more preferably not more than 2.1 mm, even more preferably not more
than 1.9 mm, and most preferably not more than 1.7 mm. If the cover
thickness is larger than the above range, the ball rebound may
decrease and the flight performance may worsen. On the other hand,
if the cover thickness is smaller than the above range, the
durability to cracking may decrease. In particular, when the ball
is hit thin, or "topped," the cover may tear.
[0094] The cover has a specific gravity which is preferably at
least 1.13, more preferably at least 1.14, and even more preferably
at least 1.15. The upper limit is preferably not more than 1.30,
more preferably not more than 1.20, and even more preferably not
more than 1.17.
[0095] The cover has a material hardness, expressed as the Shore D
hardness, of preferably at least 30, more preferably at least 35,
and even more preferably at least 38. The upper limit is preferably
not more than 57, more preferably not more than 54, even more
preferably not more than 51, and most preferably not more than 50.
If the Shore D hardness of the cover is higher than the above
range, the appearance performance in long-term use (durability of
markings) may decline, in addition to which the flight performance
may markedly decrease. On the other hand, if the Shore D hardness
of the cover is lower than the above range, the durability to
cracking may markedly decrease and, particularly when the ball is
topped, the cover may tear. In addition, the spin rate may become
very high, possibly shortening the distance traveled by the
ball.
[0096] In the invention, "Shore D hardness" refers to the hardness
measured with a type D durometer in accordance with JIS K 7215
(Durometer D hardness).
[0097] The breaking strength of the cover resin material may be set
to preferably at least 20 MPa, more preferably at least 25 MPa,
even more preferably at least 30 MPa, and most preferably at least
35 MPa. The upper limit may be set to preferably not more than 80
MPa, more preferably not more than 75 MPa, even more preferably not
more than 70 MPa, and most preferably not more than 65 MPa. The
elongation of the cover resin material may be set to preferably at
least 150%, more preferably at least 200%, even more preferably at
least 250%, and most preferably at least 300%. The upper limit may
be set to preferably not more than 600%, more preferably not more
than 550%, even more preferably not more than 520%, and most
preferably not more than 490%. The breaking strength and elongation
(tensile tests) refer to values measured in accordance with JIS K
7311-1995. By using such a cover resin material having a breaking
strength and an elongation in the above-indicated ranges, the
durability to cracking, durability to surface loss and durability
to abrasion desired of a golf ball intended for long-term use can
be improved.
[0098] The solid golf ball of the invention typically has numerous
dimples formed on the surface thereof, each dimple having a spatial
volume below a flat plane circumscribed by an edge of the dimple.
In the invention, it is critical for the sum of the individual
dimple spatial volumes, expressed as a ratio (VR) with respect to
the volume of a hypothetical sphere representing the ball were it
to have no dimples on the surface thereof, to be set to from 0.95
to 1.7. The lower limit of VR is preferably 1.0, more preferably
1.1, and most preferably 1.2. The upper limit of VR is preferably
1.6, more preferably 1.5, and most preferably 1.45.
[0099] Also, although not subject to any particular limitation, the
dimples formed on the solid golf ball of the invention preferably
satisfy conditions (1) and (2) below. Although satisfying both of
the following conditions (1) and (2) at the same time is preferred,
it is acceptable for either one of these conditions alone to be
satisfied.
[0100] First, referring to FIG. 3, as condition (1), it is
preferable for the dimples to have a peripheral edge provided with
a roundness represented by a radius of curvature R in a range of
from 0.5 to 2.5 mm. The lower limit of the radius of curvature R is
more preferably 0.55 mm, and even more preferably 0.6 mm, and the
upper limit is more preferably 1.8 mm, and even more preferably 1.5
mm.
[0101] Next, as condition (2), it is preferable for the ratio ER of
a collective number of dimples RA having a radius of curvature R to
diameter D ratio (R/D) of at least 20%, divided by the total number
of dimples N on the surface of the ball, to be in a range of from
15 to 95%. Here, the ratio R/D is expressed as a percentage
(R/D.times.100%), a larger value indicating a dimple in which the
rounded portion of the dimple accounts for a larger proportion of
the dimple size and which has a smoother cross-sectional shape. The
ratio ER indicates the number of such smooth dimples as a
proportion of the total number of dimples; by setting ER in a range
of from 15 to 95%, damage to the paint film at dimple edges can be
effectively suppressed. The upper limit in the ratio R/D is
preferably not more than 60%, and more preferably not more than
40%. The lower limit in the ratio ER is more preferably at least
20%, and even more preferably at least 25%, and the upper limit is
more preferably not more than 90%, even more preferably not more
than 85%, and most preferably not more than 70%.
[0102] In addition, although not subject to any particular
limitation, it is preferable for condition (3) below to be
satisfied. As condition (3), it is preferable for the ball to have
thereon a plurality of dimple types of differing diameter, and for
the ratio DER of a combined number of dimples DE obtained by adding
together dimples having an own diameter and having an own radius of
curvature larger than or equal to a radius of curvature of dimples
of larger diameter than the own diameter plus dimples of a type
having a largest diameter, divided by the total number N of dimples
on the surface of the ball, to be at least 80%.
[0103] Generally, at a fixed dimple depth (see FIG. 3), the radius
of curvature R representing the roundness provided to the
peripheral edges of the dimples is smaller at smaller dimple
diameters. However, above condition (3), by such means as adjusting
the depth, sets the radius of curvature R representing the
roundness of the peripheral edge to be as large as possible even in
dimples having a small diameter, thus forming dimples having a
smooth cross-sectional shape, and also increases the proportion of
such smooth dimples by setting the above ratio DER to at least 80%,
in this way more effectively suppressing damage to the paint film.
The ratio DER is more preferably at least 85%, even more preferably
at least 90%, and most preferably at least 93%. The upper limit in
the ratio DER is 100%.
[0104] In addition, the dimples on the golf ball of the invention,
although not subject to any particular limitation, preferably
satisfy conditions (4) to (6) below. Although it is preferable for
all of the following conditions (4) to (6) to be satisfied at the
same time, it is acceptable for any one of these conditions alone
to be satisfied.
[0105] As condition (4), it is preferable for the number of dimple
types of differing diameter D on the ball to be 3 or more, and more
preferable for dimples of at least five types to be formed. In this
case, the diameters D of the dimples, although not subject to any
particular limitation, are preferably set in a range of from 1.5 mm
to 7 mm, the lower limit being more preferably 1.8 mm and the upper
limit being more preferably 6.5 mm. The depths of the dimples,
although likewise not subject to any particular limitation, are
preferably set in a range of from 0.05 mm to 0.35 mm, the lower
limit being more preferably 0.1 mm, and more preferably 0.13 mm,
and the upper limit being more preferably 0.32 mm, and even more
preferably 0.29 mm.
[0106] As condition (5), the total number N of dimples on the
surface of the ball is preferably not more than 380, and more
preferably not more than 350. The total number N of dimples is even
more preferably in a range of from 220 to 340.
[0107] As condition (6), it is preferable for the dimples to be
formed in such a way that the surface coverage SR of the dimples,
which is the sum of the individual dimple surface areas, each
defined by a flat plane circumscribed by an edge of the dimple
(dash-dot line in FIG. 3), expressed as a percentage of the surface
area of a hypothetical sphere representing the ball were it to have
no dimples on the surface thereof, is from 60 to 74%. At a surface
coverage SR greater than 74%, the intervals between neighboring
dimples become too narrow, which may make it difficult to provide
the dimple edges with a roundness having the radius of curvature
specified in above condition (1). On the other hand, at a surface
coverage SR below 60%, the aerodynamic performance decreases, as a
result of which the distance traveled by the ball may decrease. The
surface coverage SR has a lower limit of more preferably 65%, and
even more preferably 68%, and an upper limit of more preferably
73%.
[0108] In one-piece golf balls, because rubber often has somewhat
of a yellow color, a white enamel paint is generally applied as a
first coat, following which a clear paint is applied. In the
inventive ball, in order to ensure a good appearance, it is
preferable to apply a clear paint to the surface of the ball. The
resulting clear coat has a thickness at dimple lands (Y) which is
at least 10 .mu.m, preferably at least 12 .mu.m, and most
preferably at least 13 .mu.m, but is not more than 30 .mu.m,
preferably not more than 25 .mu.m, and most preferably not more
than 20 .mu.m; and a thickness at dimple edges (Z) which is at
least 8 .mu.m, preferably at least 10 .mu.m, and most preferably at
least 11 .mu.m, but is not more than 28 .mu.m, preferably not more
than 23 .mu.m, and most preferably not more than 18 .mu.m. Also,
the ratio of edge areas (Z) to land areas (Y), expressed as a
percentage (Z/Y.times.100), is at least 60%, preferably at least
70%, and most preferably at least 80%, but is not more than 100%,
and preferably not more than 95%. Outside the above range, the
durability of markings at dimple edges decreases markedly in
long-term use.
[0109] The ball diameter is typically at least 42 mm, preferably at
least 42.3 mm, and more preferably at least 42.67 mm. The upper
limit in the ball diameter is preferably not more than 44 mm, more
preferably not more than 43.8 mm, even more preferably not more
than 43.5 mm, and most preferably not more than 43 mm.
[0110] The ball weight is preferably at least 44.5 g, more
preferably at least 44.7 g, even more preferably at least 45.1 g,
and most preferably at least 45.2 g. The upper limit is preferably
not more than 47.0 g, more preferably not more than 46.5 g, and
even more preferably not more than 46.0 g.
[0111] The ball has, upon initial measurement, a deflection (BH1)
when compressed under a final load of 1,275 N (130 kgf) from an
initial load of 98 N (10 kgf) of preferably at least 2.5 mm, more
preferably at least 2.6 mm, and even more preferably at least 2.65
mm. The upper limit is preferably not more than 7.0 mm, more
preferably not more than 6.0 mm, even more preferably not more than
5.5 mm, and most preferably not more than 5.0 mm. Also, letting CH
and BH1 be, respectively, the deflection by the core and the
deflection by the ball when compressed under a final load of 1,275
N (130 kgf) from an initial load of 98 N (10 kgf), the ratio CH/BH1
therebetween is preferably at least 0.95, more preferably at least
0.96, and even more preferably at least 0.97. The upper limit is
preferably not more than 1.1, more preferably not more than 1.09,
and even more preferably not more than 1.08. If the ratio CH/BH1 is
too large, the deflection of the finished ball relative to the
deflection of the core will be very small. In this case, because
the cover becomes harder, the feel at impact may decrease and the
appearance may decline with long-term use. Conversely, if the ratio
CH/BH1 is too small, the cover will be very soft, which may
significantly lower the durability to cracking and lead to cracking
of the cover, particularly when the ball is topped. In addition,
the spin rate may undergo a large increase, which may result in a
shorter distance of travel by the ball. Here, "upon initial
measurement" means when the ball is measured within about 1 month
following production of the ball.
[0112] Moreover, in the invention, the ball rebound (BV) has an
upper limit of preferably not more than 72 m/s, more preferably not
more than 71.7 m/s, even more preferably not more than 71.4 m/s,
and most preferably not more than 71.2 m/s. The lower limit is
preferably at least 60 m/s, more preferably at least 63 m/s, even
more preferably at least 66 m/s, and most preferably at least 67
m/s. As used herein, "ball rebound" is synonymous with ball initial
velocity.
[0113] In the invention, from the standpoint of ensuring durability
over an extended period of time, letting the golf ball of the
invention have, upon initial measurement, a deflection BH1 (mm)
when compressed under a final load of 1,275 N (130 kgf) from an
initial load of 98 N (10 kgf) and an initial velocity BV1 (m/s),
and letting the ball also have, when measured again after 350 days
of standing following initial measurement, a deflection BH2 (mm)
when compressed under a final load of 1,275 N (130 kgf) from an
initial load of 98 N (10 kgf) and an initial velocity BV2 (m/s),
the difference BH2-BH1 is preferably not more than 0.2 mm, more
preferably not more than 0.15 mm, and even more preferably not more
than 0.1 mm. Also, the value BV2-BV1 is preferably not more than
0.3 m/s, more preferably not more than 0.2 m/s, and even more
preferably not more than 0.1 m/s. As a result, the quality of the
ball appearance and the flight performance are maintained even in
long-term use. Here, "upon initial measurement" means when the ball
is measured within about 1 month following production of the
ball.
[0114] As described above, the solid golf ball of the invention is
endowed with the properties required of balls intended for
long-term use, including excellent durability to cracking,
durability of appearance and low-temperature scuff resistance, and
also the ability to maintain a stable feel on impact and a stable
flight performance over a long period of time.
EXAMPLES
[0115] The following Examples and Comparative Examples are provided
to illustrate the invention, and are not intended to limit the
scope thereof.
Examples 1 to 8, Comparative Examples 1 to 10
[0116] Rubber materials formulated as shown in Table 1 below were
furnished for the fabrication of solid golf balls in the examples
and comparative examples. These rubber compositions were suitably
mixed using a kneader or roll mill, then vulcanized under the
temperature and time conditions in Table 1 to produce solid cores
in the respective examples. Ingredient amounts in the table below
are shown in parts by weight.
TABLE-US-00001 TABLE 1 parts by weight (1) (2) (3) (4) (5) (6) (7)
(8) (9) (10) Core BR01 40 56 45 55 55 100 100 100 95 formulation
IR2200 5 5 20 15 5 BR730 100 SL563 55 39 55 SBR0202 25 30 Perhexa
C-40 0.6 0.6 (40% dilution) Actual amount 0.24 0.24 of addition
Percumyl D 0.8 0.8 0.8 0.9 0.9 1.2 0.8 0.6 0.6 0.8 Zinc oxide 12.3
12.8 14.8 23 22.5 23.5 23 9.5 9.5 23 Barium sulfate 9.6 9.1 7
Antioxidant 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.1 0.1 0.2 Methacrylic
acid 12 12.5 14.5 25.5 17 29 18 22.5 Zinc 26 methacrylate Zinc
acrylate 26 Titanium oxide 4 Vulcanization Temperature (.degree.
C.) 170 170 170 170 170 170 170 160 160 170 conditions Time
(minutes) 20 20 20 20 20 20 20 13 13 30
[0117] Details on the ingredients used in the core formulations in
the above table are provided below. [0118] BR01: A butadiene rubber
synthesized with a nickel catalyst, available from JSR Corporation;
Mooney viscosity ML, 46 [0119] IR2200: An isoprene rubber available
from JSR Corporation; Mooney viscosity ML, 82 [0120] BR730: A
butadiene rubber synthesized with a neodymium catalyst, available
from JSR Corporation; Mooney viscosity ML, 55 [0121] SL563: A
solution-polymerized styrene-butadiene rubber available from JSR
Corporation; styrene bond content, 20% [0122] SBR0202: An
emulsion-polymerized styrene-butadiene rubber available from JSR
Corporation; styrene bond content, 46% [0123] Perhexa C-40: An
organic peroxide available from NOF Corporation;
1,1-bis(t-butylperoxy)-cyclohexane. Because "Perhexa C-40" is a 40%
dilution, the actual amount of addition is also mentioned in the
tables. [0124] Percumyl D: An organic peroxide, available from NOF
Corporation; dicumyl peroxide [0125] Zinc oxide: Available from
Sakai Chemical Co., Ltd. [0126] Antioxidant: "Nocrac NS-6,"
available from Ouchi Shinko Chemical Industry Co., Ltd. [0127]
Methacrylic acid: Available from Kuraray Co., Ltd. [0128] Zinc
methacrylate: Available from Asada Chemical Industry Co., Ltd.
[0129] Zinc acrylate: Available from Nihon Jyoryu Kogyo Co., Ltd.
[0130] Titanium oxide: Available from Ishihara Sangyo Kaisha,
Ltd.
[0131] In each example, after the rubber composition formulated
from the ingredients shown in Table 1 was molded and vulcanized to
form a core, the surface of the core was abraded to a desired
diameter. Next, surface treatment of the core was carried out by
immersing the core for 30 seconds in an acetone solution of
trichloroisocyanuric acid (concentration, 3 wt %), then washing the
surface of the core with water. The core was then set in a mold for
injection molding the cover, and the cover composition shown in
Table 2 below was injection molded over the solid core.
TABLE-US-00002 TABLE 2 A B C Formulation (pbw) Himilan 1557 50
Himilan 1601 50 Himilan AM7327 50 Surlyn 6320 50 Pandex T8260
Pandex T8195 100 Magnesium stearate 1 1 Titanium dioxide 3.5 2.1
2.1 Polyethylene wax 1.5
[0132] Details on the ingredients in the above table are provided
below. [0133] Himilan: Ionomer resins available under this trade
name from DuPont-Mitsui Polychemicals Co., Ltd. [0134] Pandex:
Thermoplastic polyurethane elastomers available under this trade
name from DIC Bayer Polymer, Ltd. [0135] Surlyn: An ionomer resin
available under this trade name from E.I. DuPont de Nemours &
Co. [0136] Magnesium stearate: Available from NOF Corporation
[0137] Titanium dioxide: Available under the trade name "Tipaque
R550" from Ishihara Sangyo Kaisha, Ltd. [0138] Polyethylene wax:
Available under the trade name "Sanwax 161P" from Sanyo Chemical
Industries, Ltd.
[0139] In order to form a predetermined dimple pattern on the
surface of the cover, a plurality of protrusions corresponding to
the dimple pattern were formed in the mold cavity, by means of
which dimples were impressed onto the surface of the cover at the
same time that the cover was injection-molded. Details on the
dimples are given below in Table 3. The markings shown in FIG. 5
were printed on the ball surface. In addition, the ball was
clear-coated with a paint composed of 100 parts by weight of
polyester resin (acid value, 6; hydroxyl value, 168) (solids)/butyl
acetate/propylene glycol monomethyl ether acetate (PMA) in a weight
ratio of 70/15/15 as the base; 150 parts by weight of a
non-yellowing polyisocyanate, specifically an adduct of
hexamethylene diisocyanate (available from Takeda Pharmaceutical
Co., Ltd. as Takenate D-160N; NCO content, 8.5 wt %; solids
content, 50 wt %) as the curing agent; and 150 parts by weight of
butyl acetate. In Comparative Example 10, a coating of white enamel
paint was applied as a base coat for clear coating.
TABLE-US-00003 TABLE 3 Dimple Diameter D Depth R R/D N RA ER DE DER
SR VR No. Number (mm) (mm) (mm) ratio (number) (number) (%)
(number) (%) (%) (%) Configuration Dimple I 1 24 4.4 0.263 0.65 15
338 102 30 330 98 72 1.31 FIG. 4 2 204 4.2 0.252 0.65 15 3 66 3.6
0.231 0.75 21 4 12 2.7 0.170 0.8 30 5 24 2.5 0.154 0.8 32 6 8 3.4
0.160 0.45 13 Dimple II 1 24 4.4 0.287 0.6 14 338 102 30 330 98 72
1.41 FIG. 4 2 204 4.2 0.274 0.6 14 3 66 3.6 0.249 0.72 20 4 12 2.7
0.180 0.75 28 5 24 2.5 0.154 0.8 32 6 8 3.4 0.160 0.45 13 Dimple
III 1 24 4.4 0.216 0.5 11 338 36 11 306 91 72 0.99 FIG. 4 2 204 4.2
0.209 0.5 12 3 66 3.6 0.194 0.6 17 4 12 2.7 0.151 0.6 22 5 24 2.5
0.116 0.5 20 6 8 3.4 0.160 0.5 15
[0140] The abbreviations and symbols relating to dimples which
appear in Table 4 are explained below. [0141] R: Radius of
curvature representing roundness provided at the peripheral edge of
a dimple [0142] R/D ratio: Ratio of radius of curvature R to
diameter D [0143] N: Total number of dimples [0144] RA: Collective
number of dimples having an R/D ratio of at least 20% [0145] ER:
Ratio of RA to total number of dimples N [0146] DE: Sum of the
number of dimples having an own larger than or equal to a radius of
curvature of dimples of larger diameter than the own diameter, plus
the number of dimples of a type having a largest diameter [0147]
DER: Ratio of DE to the total number of dimples N [0148] SR: Sum of
individual dimple surface areas, each defined by a flat plane
circumscribed by an edge of the dimple, expressed as a percentage
of the surface area of a hypothetical sphere representing the ball
were the ball to have no dimples on the surface thereof. [0149] VR:
Sum of individual dimple spatial volumes, each formed below a flat
plane circumscribed by an edge of the dimple, expressed as a
percentage of the volume of a hypothetical sphere representing the
ball were the ball to have no dimples on the surface thereof
[0150] The physical properties of the cores and covers in the
respective examples of the invention and the comparative examples,
and the physical properties, distance, durability and feel of the
solid golf balls obtained in each example were measured or
evaluated as described below. The results are presented in Tables 4
and 5.
Deflection of Core and Finished Ball (mm)
[0151] The deflection (mm) of the core or finished ball as the test
sphere when compressed at a rate of 10 mm/min under a final load of
1,275 N (130 kgf) from an initial load of 98 N (10 kgf) was
measured. The test was performed using a model 4204 test system
from Instron Corporation.
Cross-Sectional Hardness of Core
[0152] The core was cut with a fine cutter and the JIS-C hardnesses
at above positions B to F were measured (at two places in each of
N=5 samples) in accordance with JIS K 6301-1975 after holding the
core isothermally at 23.+-.1.degree. C.
Surface Hardness of Core
[0153] JIS-C hardness measurements were carried out on the core
surface (at two places in each of N=5 samples) in accordance with
JIS K 6301-1975 after holding the core isothermally at
23.+-.1.degree. C.
Rebound (Initial Velocity) of Core and Finished Ball
[0154] The initial velocity was measured using an initial velocity
measuring apparatus of the same type as the USGA drum rotation-type
initial velocity instrument approved by the R&A. The cores or
balls used as the samples were held isothermally at a temperature
of 23.+-.1.degree. C. for at least 3 hours, then tested in a room
temperature (23.+-.2.degree. C.) chamber. Ten balls were each hit
twice, and the time taken for the cores or balls to traverse a
distance of 6.28 ft (1.91 m) was measured and used to compute the
initial velocity.
Cover Material Hardness
[0155] A cover sheet was formed and, after holding the samples
isothermally at 23.+-.1.degree. C., the Shore D hardness was
measured in accordance with ASTM D-2240.
Breaking Strength and Elongation of Cover Material (Tensile
Tests)
[0156] The material was formed into a 2 mm thick sheet, and held in
a 23.+-.1.degree. C. atmosphere for two weeks. This sample was
shaped into dumbbell-shaped test specimens in accordance with JIS K
7311-1995, and the specimens were subjected to measurement in a
23.+-.2.degree. C. atmosphere at a test rate of 5 mm/s, also in
accordance with JIS K 7311-1995. The average breaking strength and
elongation of each material were calculated from the measured
values for five specimens.
Measurement of Coating Thickness
[0157] Lands (Y): The thickness of the clear coat at land areas at
intermediate positions between dimples was measured. [0158] Edges
(Z): The thickness of the clear coat at dimple edge areas was
measured.
[0159] The above measurements were carried out at three places on
each of two balls in the respective examples, and the average of
these measurements was determined.
Distance
[0160] A TourStage X-Drive 701 (loft angle, 9.degree.),
manufactured by Bridgestone Sports Co., Ltd., was mounted as the
driver (W #1) on a golf swing robot and the ball was struck at a
head speed (HS) of 45 m/s. Both the spin rate of the ball
immediately after impact and the total distance traveled by the
ball were measured.
[0161] In addition, after the durability of markings test described
below had been carried out, the total distance of the ball was
again measured.
Durability to Cracking
[0162] The durability of the golf ball to cracking was evaluated
using an ADC Ball COR Durability Tester produced by Automated
Design Corporation (U.S.). This tester functions so as to fire a
golf ball pneumatically and cause it to repeatedly strike two metal
plates arranged in parallel. The incident velocity against the
metal plates was set at 43 m/s. The number of shots required until
cracking of the golf ball arose was measured, and the average value
for five golf balls (N=5) was determined.
Low-Temperature Scuffing
[0163] The balls were prepared by being held isothermally at a
temperature of 0.+-.1.degree. C. for at least 3 hours. Two types of
clubs were used: a TourStage X-Wedge 52.degree. and a 2008
TourStage VIQ pitching sand wedge 50.degree. with titanium face,
both manufactured by Bridgestone Sports Co., Ltd. Each club was
mounted in turn on a golf swing robot and used to strike the ball
at a head speed (HS) of 33 m/s, following which the ball was
visually examined. The ball appearance was rated according to the
following 5-point scale (results shown in the table are average
values for the two types of clubs). [0164] 5: Substantially no
damage. [0165] 4: Slight damage was apparent on surface, but was of
minimal concern. [0166] 3: Surface damage was of concern, but reuse
of ball was possible. [0167] 2: Surface was damaged with some
fraying, although reuse of ball was marginally possible. [0168] 1:
Surface was frayed, making reuse impossible.
Abrasion Test (Durability of Markings)
[0169] 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 markings and to assess the degree of
surface scratching and the degree of loss of luster due to abrasion
by the sand, as well as the degree of sand adhesion. The ball
appearance was rated as "Good," "Fair" or "NG."
Feel
[0170] Ten teaching professionals hit the test balls with a driver
(W #1) and rated the feel of the balls on impact as Good, somewhat
hard (Fair), or too hard (NG).
TABLE-US-00004 TABLE 4 Example 1 2 3 4 5 6 7 8 Core Type (1) (1)
(1) (2) (2) (2) (3) (3) Diameter, mm 39.9 39.9 39.3 39.9 39.3 39.3
39.9 41.1 Specific gravity 1.12 1.12 1.12 1.12 1.12 1.12 1.12 1.12
Deflection under 10-130 kg 5 5 5 5 5 5 4.2 4.2 compression (CH), mm
Rebound (CV), m/s 69.2 69.2 69.3 71.6 71.7 71.7 68.8 68.6 JIS-C
hardness at core surface (A) 69 69 69 70 70 70 74 74 JIS-C hardness
64 64 64 65 65 65 69 69 2 mm inside core surface (B) JIS-C hardness
66 66 66 67 67 67 71 71 5 mm inside core surface (C) JIS-C hardness
64 64 64 66 66 66 68 68 10 mm inside core surface (D) JIS-C
hardness 59 59 59 62 62 62 63 63 15 mm inside core surface (E)
JIS-C hardness at core center (F) 54 54 54 58 58 58 57 57 JIS-C
hardness difference between core 3 3 3 3 3 3 3 3 surface and 5 mm
inside core (A - C) JIS-C hardness difference between 15 15 15 12
12 12 17 17 core surface and center (A - F) Cover Type A A A A A A
A A Shore D hardness 45 45 45 45 45 45 45 45 Breaking strength, MPa
40 40 40 40 40 40 40 40 Elongation, % 360 360 360 360 360 360 360
360 Specific gravity 1.15 1.15 1.15 1.15 1.15 1.15 1.15 1.15
Thickness, mm 1.4 1.4 1.7 1.4 1.7 1.7 1.4 0.8 Finished Deflection
under 10-130 kg 4.8 4.8 4.7 4.8 4.7 4.7 4.1 4.1 ball compression 30
days after production (BH1), mm Deflection under 10-130 kg 4.7 4.7
4.6 4.7 4.6 4.6 4 4 compression 350 days after BH1 measurement
(BH2), mm Difference between BH1 and BH2, mm -0.1 -0.1 -0.1 -0.1
-0.1 -0.1 -0.1 -0.1 Rebound 30 days 68.9 68.9 68.7 71 70.8 70.8
68.5 68.9 after production (BV1), m/s Rebound 350 days 69 69 68.7
71.1 70.8 70.8 68.6 69 after BV1 measurement (BV2), m/s Difference
between BV1 and BV2, m/s 0.1 0.1 0 0.1 0 0 0.1 0.1 Diameter, mm
42.7 42.7 42.7 42.7 42.7 42.7 42.7 42.7 Core initial velocity - 0.3
0.3 0.6 0.6 0.9 0.9 0.3 -0.3 ball initial velocity (CV - BV1), ms
Core deflection/ball deflection (CH/BH1) 1.04 1.04 1.06 1.04 1.06
1.06 1.02 1.02 Dimples Type I II I II I II I II Clear Land areas
(Y), .mu.m 15 17 15 17 15 17 15 17 coat Edge areas (Z), .mu.m 13 15
13 15 13 15 13 15 thickness Coat thickness ratio (Z/Y .times. 100),
% 88 88 88 88 88 88 88 88 Distance HS 45, driver Spin rate, rpm
2920 2920 2940 2920 2940 2940 3080 3060 (30 days after Total
distance, m 192 187 191 194 198 193 190 185 production) HS 45,
driver Total distance, m 189 184 188 191 195 190 187 182 (after
abrasion test) Distance Total distance, m -3 -3 -3 -3 -3 -3 -3 -3
difference Durability Durability to At incident 930 930 1080 930
1080 1080 1010 860 cracking velocity of 43 m/s Low-temperature HS,
38 m/s 3 3 3 4 4 4 3 3 scuffing (at 0.degree. C.) Abrasion test
After 144 hours good good good good good good good good (durability
of of sand abrasion markings) Feel Driver good good good good good
good good good
TABLE-US-00005 TABLE 5 Comparative Example 1 2 3 4 5 6 7 8 9 10
Core Type (4) (5) (5) (5) (5) (5) (6) (8) (9) (10) Diameter, mm
39.9 39.9 39.9 39.9 37.3 42.3 39.9 39.9 39.9 42.7 Specific gravity
1.12 1.12 1.12 1.12 1.12 1.12 1.13 1.12 1.12 1.12 Deflection under
10-130 kg 4 5 5 5 5 5 1.8 3.8 3.8 compression (CH), mm Rebound
(CV), m/s 67.7 69.7 69.7 69.7 69.7 69.7 73.7 77 77.4 JIS-C hardness
at core surface (A) 71 64 64 64 64 64 90 70 70 80 JIS-C hardness 66
59 59 59 59 59 88 65 65 75 2 mm inside core surface (B) JIS-C
hardness 68 61 61 61 61 61 87 68 68 77 5 mm inside core surface (C)
JIS-C hardness 66 61 61 61 61 61 81 66 66 71 10 mm inside core
surface (D) JIS-C hardness 63 59 59 59 59 59 74 62 62 67 15 mm
inside core surface (E) JIS-C hardness at core center (F) 59 55 55
55 55 55 70 58 58 63 JIS-C hardness difference between core 3 3 3 3
3 3 3 2 2 3 surface and 5 mm inside core (A - C) JIS-C hardness
difference between 12 9 9 9 9 9 20 12 12 17 core surface and center
(A - F) Cover Type A A B C A A A A A Shore D hardness 45 45 60 45
45 45 45 45 45 Breaking strength, MPa 40 40 17 12 40 40 40 40 40
Elongation, % 360 360 100 120 360 360 360 360 360 Specific gravity
1.15 1.15 0.99 0.99 1.15 1.15 1.15 1.15 1.15 Thickness, mm 1.4 1.4
1.4 1.4 2.7 0.2 1.4 1.4 1.4 Finished Deflection under 10-130 kg 3.8
4.75 4.3 4.85 4.35 5 1.9 3.8 3.8 3.1 ball compression 30 days after
production (BH1), mm Deflection under 10-130 kg 3.7 4.65 4.2 4.75
4.25 5 1.9 3.5 3.5 3.1 compression 350 days after BH1 measurement
(BH2), mm Difference between BH1 and BH2, mm -0.1 -0.1 -0.1 -0.1
-0.1 0 0 -0.3 -0.3 0 Rebound 30 days 67.3 69.1 68.9 68.5 68.1 69.4
73 76 76.4 74.6 after production (BV1), m/s Rebound 350 days 67.4
69.1 69.1 68.6 68.1 69.4 73 75.1 75.5 74.7 after BV1 measurement
(BV2), m/s Difference between BV1 and BV2, m/s 0.1 0 0.2 0.1 0 0 0
-0.9 -0.9 0.1 Diameter, mm 42.7 42.7 42.7 42.7 42.7 42.7 42.7 42.7
42.7 42.7 Core initial velocity - 0.4 0.6 0.8 1.2 1.6 0.3 0.7 1.0
1.0 ball initial velocity (CV - BV1), ms Core deflection/ball
deflection (CH/BH1) 1.05 1.05 1.16 1.03 1.15 1.00 0.95 1.00 1.00
Dimples Type I I I I III I I I I I Clear Land areas (Y), .mu.m 15
15 15 15 17 15 15 15 15 15 coat Edge areas (Z), .mu.m 13 13 13 13 8
13 13 13 13 13 thickness Coat thickness ratio (Z/Y .times. 100), %
88 88 88 88 47 88 88 88 88 88 Distance HS 45, driver Spin rate, rpm
3180 2960 2900 3050 2610 3210 3480 3100 3070 3650 (30 days after
Total distance, m 187 193 192 190 194 193 212 225 227 219
production) HS 45, driver Total distance, m 184 190 185 184 187 190
209 222 224 213 (after abrasion test) Distance Total distance, m -3
-3 -7 -6 -7 -3 -3 -3 -3 -6 difference Durability Durability to At
incident 1035 930 940 610 1530 630 1425 555 520 620 cracking
velocity of 43 m/s Low-temperature HS, 38 m/s 1 1 3 1 1 1 3 4 4 5
scuffing (at 0.degree. C.) Abrasion test After 144 hours good good
NG NG NG good good good good NG (durability of of sand abrasion
markings) Feel Driver good good NG good good good NG good good
good
[0171] From the results in Tables 4 and 5, the comparative examples
were confirmed, as shown below, to be inferior to the working
examples of the invention.
[0172] In the golf ball of Comparative Example 1, styrene-butadiene
rubber having a high styrene bond content (trade name: SBR0202) was
used, as a result of which the scuff resistance at low temperature
was poor.
[0173] In the golf ball of Comparative Example 2, styrene-butadiene
rubber having a high styrene bond content (trade name: SBR0202) was
used, as a result of which the scuff resistance at low temperature
was poor.
[0174] In the golf ball of Comparative Example 3, the cover had a
small breaking strength and a small elongation, as a result of
which the durability to abrasion was poor and the decrease in
flight performance was large. In addition, the cover was hard, as a
result of which the feel at impact with a driver was poor.
[0175] In the golf ball of Comparative Example 4, the cover had a
small breaking strength and a small elongation, as a result of
which the durability to abrasion was poor and the decrease in
flight performance was large.
[0176] In the golf ball of Comparative Example 5, styrene-butadiene
rubber having a high styrene bond content (trade name: SBR0202) was
used, as a result of which the scuff resistance at low temperature
was poor. In addition, the dimple edges had a small radius of
curvature R, as a result of which the abrasion durability was poor
and the decrease in flight performance was large.
[0177] In the golf ball of Comparative Example 6, styrene-butadiene
rubber having a high styrene bond content (trade name: SBR0202) was
used, as a result of which the scuff resistance at low temperature
was poor. In addition, the cover was too thin, as a result of which
the durability to cracking decreases.
[0178] In the golf ball of Comparative Example 7, the core
deflection was very small, as a result of which the feel at impact
with a driver was very poor.
[0179] In the golf ball of Comparative Example 8, the core included
zinc methacrylate. As a result, the changes over time in deflection
and rebound were large, in addition to which the durability to
cracking was poor.
[0180] In the golf ball of Comparative Example 9, the core included
zinc acrylate. As a result, the changes over time in deflection and
rebound were large, in addition to which the durability to cracking
was poor.
[0181] The golf ball of Comparative Example 10 had a one-piece
construction in which the surface rubber material had a small
breaking strength and a small elongation. As a result, the
durability to cracking and the durability to abrasion were both
poor, and the ball exhibited a large decline in flight performance
(the rubber material had a breaking strength of 15 MPa and an
elongation of 88%).
* * * * *