U.S. patent application number 10/003770 was filed with the patent office on 2003-05-29 for golf ball comprising higher coefficient of restitution core and method of making same.
This patent application is currently assigned to SPALDING SPORTS WORLDWIDE, INC.. Invention is credited to Nesbitt, R. Dennis.
Application Number | 20030100384 10/003770 |
Document ID | / |
Family ID | 21707500 |
Filed Date | 2003-05-29 |
United States Patent
Application |
20030100384 |
Kind Code |
A1 |
Nesbitt, R. Dennis |
May 29, 2003 |
Golf ball comprising higher coefficient of restitution core and
method of making same
Abstract
The present invention is directed to a golf ball including a
solid, molded core formed from a core composition having a
polybutadiene rubber exhibiting a solution viscosity greater than
70 mPa.s, preferably greater than about 80 mPa.s, and more
preferably greater than about 100 mPa.s. The core preferably
exhibits a coefficient of restitution of at least about 0.780. The
present invention is also directed to methods for making
compositions having particular coefficient of restitution values
formed from polybutadiene rubbers with solution viscosity values
related to the coefficient of restitution value of the composition.
As the solution viscosity for the polybutadiene rubber has a higher
value, the coefficient of restitution of the core also increases.
Preferably, a solid, molded core is formed from the present method,
and/or a golf ball comprising such a core.
Inventors: |
Nesbitt, R. Dennis;
(Westfield, MA) |
Correspondence
Address: |
MICHELLE BUGBEE, ASSOCIATE PATENT COUNSEL
SPALDING SPORTS WORLDWIDE INC
425 MEADOW STREET
PO BOX 901
CHICOPEE
MA
01021-0901
US
|
Assignee: |
SPALDING SPORTS WORLDWIDE,
INC.
|
Family ID: |
21707500 |
Appl. No.: |
10/003770 |
Filed: |
November 15, 2001 |
Current U.S.
Class: |
473/371 |
Current CPC
Class: |
A63B 37/0003 20130101;
A63B 37/0061 20130101; A63B 37/06 20130101 |
Class at
Publication: |
473/371 |
International
Class: |
A63B 037/04; A63B
037/06 |
Claims
Having thus described the preferred embodiments, the invention is
now claimed to be:
1. A golf ball comprising: a solid core formed from a core
composition including a polybutadiene rubber exhibiting a solution
viscosity of at least about 90 mPa.s.
2. The golf ball of claim 1, wherein said core exhibits a
coefficient of restitution of at least about 0.780.
3. The golf ball of claim 2, wherein said solution viscosity value
of said polybutadiene rubber is related to said coefficient of
restitution value of said core so that the higher the value of said
solution viscosity, the higher the value of said coefficient of
restitution.
4. The golf ball of claim 3, wherein said polybutadiene rubber
exhibits a Mooney viscosity of from about 38 to about 52.
5. The golf ball of claim 1, wherein said golf ball also comprises
a cover covering the core, wherein the cover has one or more
layers.
6. The golf ball of claim 1, wherein said polybutadiene rubber has
a cis-1,4 content of at least about 96%.
7. The golf ball of claim 1, wherein said core further comprises a
second polybutadiene rubber.
8. The golf ball of claim 1, wherein said polybutadiene rubber has
a solution viscosity of at least about 130 mPa.s.
9. The golf ball of claim 2, wherein said core exhibits a
coefficient of restitution of at least about 0.785.
10. A golf ball comprising: a solid, molded core formed from a core
composition including a polybutadiene rubber exhibiting a solution
viscosity of at least about 90 mPa.s, said core exhibiting a
coefficient of restitution of at least about 0.783.
11. The golf ball of claim 10, wherein said polybutadiene rubber
has a cis-1,4 content of at least about 96%.
12. The golf ball of claim 10, wherein said solution viscosity
value of said polybutadiene rubber is related to said coefficient
of restitution value of said core so that the higher the value of
said solution viscosity, the higher the value of said coefficient
or restitution.
13. The golf ball of claim 10, wherein said core further comprises
a second polybutadiene rubber.
14. The golf ball of claim 10, wherein said polybutadiene rubber
exhibits a Mooney viscosity of from about 38 to about 52.
15. The golf ball of claim 10, wherein said polybutadiene rubber
has a solution viscosity of at least about 130 mPa.s.
16. A method for making a molded core exhibiting a particular
coefficient of restitution value comprising: selecting a
polybutadiene rubber exhibiting a particular solution viscosity
value; and forming a core from said polybutadiene rubber, said core
exhibiting a coefficient of restitution value related to the value
of said solution viscosity of said polybutadiene rubber.
17. A core formed from the method of claim 16.
18. The method of claim 16, wherein the value of said coefficient
of restitution of said core is higher as the value of said solution
viscosity exhibited by said polybutadiene rubber is increased.
19. The method of claim 16, wherein said polybutadiene rubber
exhibits a Mooney viscosity of from about 38 to about 52.
20. The method of claim 16, wherein said polybutadiene rubber
exhibits a solution viscosity of at least about 90 mPa.s.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to golf balls including
improved polybutadiene compositions for use in producing molded
golf ball cores. Additionally, the present invention is directed to
golf balls including a molded core formed from a polybutadiene
rubber exhibiting a solution viscosity value that is correlated to
the coefficient of restitution value of the molded core. The
present invention is also directed to cores and/or golf balls
produced by utilizing such a correlation, and/or to methods of
making the same.
BACKGROUND OF THE INVENTION
[0002] The composition of a golf ball core affects the properties
of a golf ball in many ways. Particularly, the golf ball core
composition affects the playability and durability properties of a
golf ball. Currently, golf ball cores are typically formed from a
synthetic polybutadiene rubber composition. The polybutadiene
rubber composition provides resilience to the golf ball, while also
providing many desirable properties to both the core and golf ball,
including weight, compression, coefficient of restitution (C.O.R.),
etc.
[0003] The C.O.R. is a particularly important golf ball property.
The resilience or C.O.R. of a golf ball is the constant "e," which
is the ratio of the relative velocity of an elastic sphere after
direct impact to that before impact. In other words, the C.O.R. is
the ratio of the outgoing velocity to the incoming velocity. As a
result, the C.O.R. ("e") can vary from 0 to 1, with 1 being
equivalent to a perfectly or completely elastic collision and 0
being equivalent to a perfectly or completely inelastic
collision.
[0004] The C.O.R. in solid core golf balls is a function of the
composition of the molded core and cover. The molded core and/or
cover may be comprised of one or more layers such as in
multi-layered balls. In balls containing a wound core (i.e., balls
comprising a liquid or solid center, elastic windings, and a
cover), the coefficient of restitution is a function of not only
the composition of the center and cover, but also the composition
and tension of the elastomeric windings. As in the solid core
balls, the center and cover of a wound core ball may also consist
of one or more layers.
[0005] C.O.R., along with additional factors such as club head
speed, club head mass, ball weight, ball size and density, spin
rate, angle of trajectory and surface configuration (i.e., dimple
pattern and area of dimple coverage) as well as environmental
conditions (e.g. temperature, moisture, atmospheric pressure, wind,
etc.) generally determine the distance a ball will travel when hit.
Along this line, the distance a golf ball will travel under
controlled environmental conditions is a function of the speed and
mass of the club and size, density and resilience (C.O.R.) of the
ball and other factors. The initial velocity of the club, the mass
of the club and the angle of the ball's departure are essentially
provided by the golfer upon striking. Since club head, club head
mass, the angle of trajectory and environmental conditions are not
determinants controllable by golf ball producers, and the ball size
and weight are set by the United States Golf Association
(U.S.G.A.), these are not factors of concern among golf ball
manufacturers. The factors or determinants of interest with respect
to improved distance are generally the coefficient of restitution
(C.O.R.) and the surface configuration (dimple pattern, ratio of
land area to dimple area, etc.) of the golf ball.
[0006] There is no U.S.G.A. limit on the C.O.R. of a golf ball, but
the initial velocity of the golf ball must not exceed 255 feet per
second. As a result, the industry goal for initial velocity is 255
feet per second, and the industry strives to maximize the C.O.R.
without violating this limit. Having the longest ball--compatible
with the U.S.G.A. requirements--has been and also remains another
longstanding objective of golf ball manufacturers. In this respect,
prior balata and polymeric covered balls, and certainly those
intended for U.S.G.A. regulation play, have shared one thing in
common. They have all relied on their preformed cores as the
primary vehicle for transferring energy from the golf club to the
ball when the ball is struck by the club. For years, the principal
thrust of golf ball research and development has been directed to
making improved preformed cores for enhancing distance performance.
In other words, conventional wisdom among golf ball manufacturers
has been that enhanced distance performance is primarily achievable
through cores formed from improved core compositions.
[0007] The C.O.R. must be carefully controlled in all commercial
golf balls if the ball is to be within the specifications regulated
by the U.S.G.A. As mentioned to some degree above, the U.S.G.A.
standards indicate that a "regulation" ball cannot have an initial
velocity exceeding 255 feet per second in an atmosphere of
75.degree. F. when tested on a U.S.G.A. machine. Since the C.O.R.
of a ball is related to the ball's initial velocity, it is highly
desirable to produce a ball having sufficiently high C.O.R. to
closely approach the U.S.G.A. limit on initial velocity, while
having an ample degree of softness (i.e., hardness) to produce
enhanced playability (i.e., spin, etc.).
[0008] Present core compositions in golf balls are typically formed
from polybutadiene rubbers under the TAKTENE.RTM. (Bayer AG) or
CARIFLEX.RTM. (Shell Chemical) trademark designations, including
under the particular TAKTENE.RTM. 220 and CARIFLEX.RTM. BR-1220
polybutadiene rubber designations. TAKTENE.RTM. or CARIFLEX.RTM.
polybutadiene compositions and the core compositions formed from
those polybutadiene rubbers exhibit well-known properties,
including P.G.A. and Riehle compression, solution viscosity and
C.O.R. properties. The properties of TAKTENE.RTM. or CARIFLEX.RTM.
polybutadiene rubbers and the core compositions formed from these
polybutadiene rubbers, however, are within a particular well known
range, and thus, the properties are limited if one desired a core
composition having improved properties outside of these known
property ranges.
[0009] Due to the continuous importance of improving the properties
of a golf ball, particularly the C.O.R. of a golf ball, it would be
beneficial to form a golf ball core composition from a
polybutadiene rubber that exhibits improved properties,
particularly improved C.O.R., over known golf ball core
compositions. It would also be beneficial to be able to exhibit a
particular C.O.R. for a core composition based upon a particular
property within the polybutadiene rubber.
SUMMARY OF THE INVENTION
[0010] The present invention relates to golf ball cores having a
particular C.O.R. value formed from a polybutadiene rubber having a
particular solution viscosity and methods for making such cores.
The polybutadiene rubber that forms the composition exhibits a
particular solution viscosity value that is related to the C.O.R.
value of the resulting molded core, so that the higher the solution
viscosity value of the polybutadiene rubber, the higher the C.O.R.
value of the core. This is while the solid Mooney viscosity of the
polybutadiene rubber remains relatively constant.
[0011] The present invention further relates to golf balls
including a core formed from a composition having a polybutadiene
rubber exhibiting a solution viscosity that is directly related to
the C.O.R. value of the finished molded core, and methods for
making such a golf ball. As previously stated, it has been found
that at a constant Mooney viscosity, the higher the solution
viscosity of the polybutadiene rubber, the higher the C.O.R. value
of the resulting molded core. Therefore, the present invention also
relates to higher C.O.R. cores formed from core compositions having
higher solution viscosities than other known core formulations, at
similar solid Mooney viscosities and methods for forming and/or
producing such cores.
[0012] In an additional aspect, the present invention is directed
to golf balls comprising a core formed from a polybutadiene rubber.
The polybutadiene rubber exhibits a solution viscosity of greater
than 70 mPa.s, preferably greater than 80 mPa.s, and more
preferably greater than 90 mPa.s, at a constant solid Mooney
viscosity of about 38 to about 52, preferably about 45.+-.5. The
golf ball also includes one or more core and/or cover layers
generally surrounding the core, either alone or in combination with
other layers of materials.
[0013] In a further aspect, the present invention is directed to
golf balls comprising a core formed from a core composition
including a polybutadiene rubber exhibiting a solution viscosity of
about 90 mPa.s, preferably of about 100 mPa.s, and most preferably
about 130 mPa.s at a relatively constant solid Mooney viscosity of
45.+-.5, preferably about 45. The molded core exhibits a
coefficient of restitution of at least about 0.783.
[0014] In another aspect, the present invention is directed to a
golf ball comprising a core formed from a core composition
including a polybutadiene rubber. The polybutadiene rubber exhibits
a solution viscosity of at least about 100 mPa.s and a Mooney
viscosity of from about 38 to about 52. The core exhibits a
coefficient of restitution of at least about 0.785. The value of
the coefficient of restitution of the core is related to the value
of the solution viscosity of the polybutadiene rubber. The golf
ball further includes one or more core or cover layers disposed
about the core.
[0015] In yet another aspect, the present invention is directed to
a method for making a molded golf ball core having a particular
coefficient of restitution (C.O.R.) value, and the golf balls
produced thereby. The method includes selecting a polybutadiene
rubber exhibiting a particular solution viscosity value that is
correlated to the particular C.O.R. value desired. The method
further includes forming a composition from that polybutadiene
rubber so that the composition, when molded into a solid core, has
a coefficient of restitution value related to the value of the
solution viscosity of the polybutadiene rubber. The method further
comprises the step of covering the core so formed with one or more
core or cover layers.
[0016] In yet a further aspect, the present invention is directed
to a method for making a solid golf ball core. The method includes
selecting a polybutadiene rubber exhibiting a particular solution
viscosity value. A core composition is formed including the
polybutadiene rubber. A molded, solid core is formed from the core
composition, and the core exhibits a coefficient of restitution
(C.O.R.) value related to the solution viscosity value of the
polybutadiene rubber. If desired, one or more core and/or cover
layers enclose such a core. The present invention also relates to
golf balls formed by this method.
[0017] Other features and benefits of the present invention will
come to light in reviewing the following written specification and
accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The foregoing and other objects, features and advantages of
the present invention should become apparent in the following
description when taken in conjunction with the accompanying
drawing, in which:
[0019] FIG. 1 shows a graph of coefficient of restitution values
for each different core versus solution viscosity values for the
polybutadiene rubbers that form each core.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The present invention is directed to a golf ball comprising
a core produced from an improved core composition. The core
composition includes a base polybutadiene rubber exhibiting
enhanced solution viscosity values which, when utilized for golf
ball core construction, produce cores exhibiting an enhanced C.O.R.
over known core compositions. The present invention is also
directed to methods for making such compositions, particularly,
core compositions, having enhanced C.O.R values when utilized in
golf ball construction.
[0021] The present invention is also directed to a golf ball
comprising a core formed from a core composition including a
polybutadiene rubber. The polybutadiene rubber exhibits a higher
solution viscosity (at a relatively constant solid Mooney
viscosity) over known polybutadiene rubbers used in core
compositions. Preferably, the polybutadiene rubber exhibits a
solution viscosity of greater than 70 mPa.s, preferably greater
than about 80 mPa.s, and more preferably greater than about 90
mPa.s, at a constant solid Mooney viscosity of about 38 to about
52, more preferably 45.+-.5.
[0022] Further preferably, the polybutadiene rubber in the core
composition exhibits a solution viscosity of at least about 100
mPa.s and a Mooney viscosity of from about 38 to about 52. The core
formed from the core composition has a coefficient of restitution
of at least about 0.783, preferably about 0.785 or more.
[0023] Most preferably, the present invention is directed to a
solid, non-wound, golf ball comprising a solid, molded core formed
from a core composition including polybutadiene rubber. The
polybutadiene rubber exhibits a solution viscosity of about 130
mPa.s and a Mooney viscosity of from about 38 to about 52. The core
that is formed from the core composition exhibits a coefficient of
restitution (C.O.R.) of at least about 0.785. The value of the
solution viscosity of the polybutadiene rubber is related to the
coefficient of restitution value of the core in such a manner such
that the higher the value of the solution viscosity of the
polybutadiene rubber, the higher the value of the coefficient of
restitution of the solid, molded core formed from such
polybutadiene rubber. The Mooney viscosity of the polybutadiene
rubber utilized to form the core remains relatively constant.
[0024] The solution viscosity for the polybutadiene rubbers is
defined according to the standard ASTM D 445-01, herein
incorporated by reference. Solution viscosity values throughout the
present application are defined with the units of mPa.s. The
solution viscosity can also be defined under other known
international standards including DIN 51 562.
[0025] The Mooney viscosity (ML (1+4) 100.degree. C.) value for the
polybutadiene rubber is defined according to the standard ASTM D
1646-00, herein incorporated by reference. The Mooney viscosity for
the polybutadiene can also be defined under other accepted
international standards, including ISO 289 and DIN 53 523.
[0026] In another embodiment, the core composition can be formed
from a single polybutadiene rubber or a blend of two or more
polybutadiene rubbers, or a blend of polybutadiene rubber with
other elastomers. When the core composition is formed from a blend
of two or more polybutadiene rubbers, at least one of the
polybutadiene rubbers preferably exhibits a solution viscosity of
greater than 70 mPa.s, preferably 80 mPa.s and more preferably 90
mPa.s, at a relatively constant solid Mooney viscosity of about 38
to about 52, preferably 45.+-.5. The molded core has a coefficient
of restitution of at least about 0.780, preferably about 0.785 or
more.
[0027] The relationship between the solution viscosity and the
coefficient of restitution is valuable when it is desired to
achieve particular properties in a golf ball, such as a particular
coefficient of restitution for the core based upon solution
viscosity values for a particular polybutadiene rubber or blend of
polybutadiene rubbers. Also, a higher coefficient of restitution
value for the molded core can be achieved by forming the core from
a core composition including a polybutadiene rubber or blends of
polybutadiene rubbers having a higher solution viscosity value.
[0028] While the solution viscosity values for the polybutadiene
rubbers used in the present invention can vary, the solid Mooney
viscosity of the polybutadiene rubbers remains relatively constant.
As used herein, a relatively constant solid Mooney viscosity value
for the polybutadiene rubber means a value within a particular
range of values. Preferably, the polybutadiene rubber exhibits a
Mooney viscosity of from about 38 to about 52. More preferably, the
polybutadiene rubber exhibits a Mooney viscosity of from about 40
to about 50, i.e. 45.+-.5. Thus, as the preferred solid Mooney
viscosity values exhibited by the polybutadiene rubbers remain
relatively constant, the solution viscosity values for the
polybutadiene rubbers can vary greatly. This is discussed in more
detail below.
[0029] Preferably, the polybutadiene rubbers used in the present
invention have a high cis-1,4 content. The preferred polybutadiene
rubbers have a cis-1,4 content of at least about 96%.
[0030] The preferred polybutadiene rubbers for the core composition
are the commercially available BUNA.RTM. CB series polybutadiene
rubbers manufactured by the Bayer Co., Pittsburgh, Pa. The
BUNA.RTM. CB series polybutadiene rubbers are generally of a
relatively high purity and light color. The low gel content of the
BUNA.RTM. CB series polybutadiene rubbers ensures almost complete
solubility in styrene. The BUNA.RTM. CB series polybutadiene
rubbers have a relatively high cis-1,4 content. Preferably, each
BUNA.RTM. CB series polybutadiene rubber has a cis-1,4 content of
at least 96%. Additionally, each BUNA.RTM. CB series polybutadiene
rubber exhibits a different solution viscosity, preferably from
about 42 mPa.s to about 170 mPa.s, while maintaining a relatively
constant solid Mooney viscosity value range, preferably of from
about 38 to about 52. The BUNA.RTM. CB series polybutadiene rubbers
preferably have a vinyl content of less than about 12%, more
preferably a vinyl content of about 2%. Table 1 below discloses the
commercially available BUNA.RTM. CB series polybutadiene rubbers
and the solution viscosity and Mooney viscosity of each BUNA.RTM.
CB series polybutadiene rubber.
1TABLE 1 Solution Viscosity and Mooney Viscosity of BUNA .RTM. CB
Series Polybutadiene Rubbers BUNA .RTM. CB BUNA .RTM. CB BUNA .RTM.
CB BUNA .RTM. CB BUNA .RTM. CB Property 1405 1406 1407 1409 1410
Solution 50 60 70 90 100 Viscosity +/-7 +/-7 +/-10 +/-10 +/-10 mPa
.multidot. s Mooney 45 45 45 45 45 Viscosity +/-5 +/-5 +/-5 +/-5
+/-5 mL 1 + 4 100.degree. C. BUNA .RTM. CB BUNA .RTM. CB BUNA .RTM.
CB BUNA .RTM. CB BUNA .RTM. CB Property 1412 1414 1415 1416 10
Solution 120 140 150 160 140 Viscosity +/-10 +/-10 +/-10 +/-10
+/-20 mPa .multidot. s Mooney 45 45 45 45 47 Viscosity +/-5 +/-5
+/-5 +/-5 +/-5 mL 1 + 4 100 .degree. C.
[0031] Table 2 below further shows other properties exhibited by
BUNA.RTM. CB 1406, BUNA.RTM.CB 1407, BUNA.RTM. CB 1409, BUNA.RTM.
CB 1410, BUNA.RTM. CB 1412, BUNA.RTM. CB 1414, BUNA.RTM. CB 1415,
and BUNA.RTM. CB 1416.
2TABLE 2 BUNA .RTM. BUNA .RTM. BUNA .RTM. BUNA .RTM. Property Test
Method Units CB 1406 CB 1407 CB 1409 CB 1410 Catalyst Cobalt Cobalt
Cobalt Cobalt Cis-1,4 IR % .gtoreq.96 .gtoreq.96 .gtoreq.96
.gtoreq.96 Content Spectroscopy; AN-SAA 0422 Volatile ISO 248/ %
.ltoreq.0.5 .ltoreq.0.5 .ltoreq.0.5 .ltoreq.0.5 Matter ASTM D 1416
Ash Content ISO 247/ % .ltoreq.0.1 .ltoreq.0.1 .ltoreq.0.1
.ltoreq.0.1 ASTM D 1416 Mooney ISO 289/DIN MU 45 .+-. 5 45 .+-. 5
45 .+-. 5 45 .+-. 5 Viscosity ML 53 523/ASTM (1 + 4) 100.degree. C.
D 1646 Solution ASTM D 445/ mPa .multidot. s 60 .+-. 7 70 .+-. 7 90
.+-. 10 100 .+-. 10 Viscosity, 5% DIN 51 562 in styrene Styrene
08-02.08.CB ppm .ltoreq.100 .ltoreq.100 .ltoreq.100 .ltoreq.100
insoluble: dry gel Color in ISO 6271/ APHA .ltoreq.10 .ltoreq.10
.ltoreq.10 .ltoreq.10 styrene ASTM D 1209 Solubility in in in in
aliphatic aliphatic aliphatic aliphatic hydro- hydro- hydro- hydro-
carbons carbons carbons carbons Total Amount AN-SAA 0583 % 0.2 0.2
0.2 0.2 of Stabilizer BUNA .RTM. BUNA .RTM. BUNA .RTM. BUNA .RTM.
Property Test Method Units CB 1412 CB 1414 CB 1415 CB 1416 Catalyst
Cobalt Cobalt Cobalt Cobalt Cis-1,4 IR % .gtoreq.96 .gtoreq.96
.gtoreq.96 .gtoreq.96 Content Spectroscopy; AN-SAA 0422 Volatile
ISO 248/ % .ltoreq.0.5 .ltoreq.0.5 .ltoreq.0.5 .ltoreq.0.5 Matter
ASTM D 1416 Ash Content ISO 247/ % .ltoreq.0.1 .ltoreq.0.1
.ltoreq.0.1 .ltoreq.0.1 ASTM D 1416 Mooney ISO 289/DIN MU 45 .+-. 5
45 .+-. 5 45 .+-. 5 45 .+-. 5 Viscosity ML 53 523/ASTM (1 + 4)
100.degree. C. D 1646 Solution ASTM D 445/ mPa .multidot. s 120
.+-. 10 140 .+-. 10 150 .+-. 10 160 .+-. 10 Viscosity, 5% DIN 51
562 in styrene Styrene 08-02.08.CB ppm .ltoreq.100 .ltoreq.100
.ltoreq.100 .ltoreq.100 insoluble:dry gel Color in ISO 6271/ APHA
.ltoreq.10 .ltoreq.10 .ltoreq.10 .ltoreq.10 styrene ASTM D 1209
Solubility in in in in aliphatic aliphatic aliphatic aliphatic
hydro- hydro- hydro- hydro- carbons carbons carbons carbons Total
Amount AN-SAA 0583 % 0.2 0.2 0.2 0.2 of Stabilizer
[0032] Of the above described BUNA.RTM. CB polybutadiene rubbers,
the most preferred for a core composition is BUNA.RTM. CB 10
polybutadiene rubber. BUNA.RTM. CB 10 polybutadiene rubber has a
relatively high cis-1,4 content, good resistance to aging,
reversion, abrasion and flex cracking, good low temperature
flexibility and high resilience. The BUNA.RTM. CB 10 polybutadiene
rubber preferably has a vinyl content of less than about 12%, more
preferably about 2% or less. Table 3 below shows the specific
properties of the BUNA.RTM. CB 10 polybutadiene rubber.
3TABLE 3 Properties of BUNA .RTM. CB 10 Polybutadiene Rubber Value
Unit Test method Raw Material Properties Volatile Matter
.ltoreq.0.5 wt-% ISO 248/ASTM D 5668 Mooney viscosity ML (1 + 4) @
47 .+-. 5 MU ISO 289/ASTM D 1646 100.degree. C. Solution viscosity,
5.43 wt % 140 .+-. 20 mPa .multidot. s ASTM D 445/ISO 3105 in
toluene (5% in toluene) Cis-1,4 content .gtoreq.96 wt-% IR
Spectroscopy, AN SAA 0422 Color, Yellowness Index .ltoreq.10 ASTM E
313-98 Cobalt content .ltoreq.5 ppm DIN 38 406 E22 Total Stabilizer
content .gtoreq.0.15 wt-% AN-SAA 0583 Specific Gravity 0.91
Vulcanization Properties (Test formulation from ISO 2476/ ASTM D
3189 (based on IRB 7)) Monsanto Rheometer MDR 2000E, 160.degree.
C./30 min./.alpha. = .+-.0.5.degree. C. Torque Minimum (ML) 3.5
.+-. 0.7 dNm ISO 6502/ASTM D5289 Torque Maximum (MH) 19.9 .+-. 2.4
dNm ISO 6502/ASTM D5289 Scorch Time, t.s..sub.1 2.9 .+-. 0.6 min
ISO 6502/ASTM D5289 Cure Time, t.c..sub.50 8.7 .+-. 1.7 min ISO
6502/ASTM D5289 Cure Time, t.c..sub.90 12.8 .+-. 2.4 min ISO
6502/ASTM D5289
[0033] A core composition can include one BUNA.RTM. CB series
polybutadiene rubber or a blend of two or more BUNA.RTM. CB series
polybutadiene rubbers. Alternatively, the BUNA.RTM. CB series
polybutadiene rubbers may be blended with one or more other
polybutadiene rubbers in forming the core composition. Other
preferred polybutadiene rubbers that can be blended with the
BUNA.RTM. CB series polybutadiene rubbers include commercially
available polybutadiene rubbers under the designation NEO CIS.RTM.
40 and NEO CIS.RTM. 60 polybutadiene rubbers, available from
Enichem Elastomers America, Inc., Houston Tex.
[0034] Blends of BUNA.RTM. CB series polybutadiene rubbers and
other polybutadiene rubbers can include from 1 to 99 weight % of
the BUNA.RTM. CB series polybutadiene rubber and from 99 to 1
weight % of a second polybutadiene rubber. The second polybutadiene
rubber can be a second BUNA.RTM. CB series polybutadiene rubber or
a polybutadiene rubber different from the BUNA.RTM. CB series
polybutadiene rubbers. Preferably, the blend of BUNA.RTM. CB series
polybutadiene rubber with a second polybutadiene rubber includes at
least 50 weight % of a BUNA.RTM. CB series polybutadiene rubber and
50 weight % or less of a second polybutadiene rubber. Most
preferably, the blend of polybutadiene rubbers includes at least 70
weight % of a BUNA.RTM. CB series polybutadiene rubber and 30
weight % or less of a second polybutadiene rubber.
[0035] The golf ball core is preferably formed from a cross-linked
unsaturated elastomer and comprises a polybutadiene rubber. The
diameter of the core is determined based upon the desired ball
diameter minus the thickness of the cover layer or layers (if
desired). The core generally has a diameter of about 1.0 to 1.6
inches, preferably about 1.4 to 1.6 inches.
[0036] Conventional solid cores are typically compression molded
from slugs of uncured or slightly cured elastomer composition
including a high cis-1,4 content polybutadiene. A small amount of a
metal oxide, such as zinc oxide, may be included as a filler. Large
amounts of metal oxide may be included in conventional cores in
order to increase the core weight so that the finished ball more
closely approaches the U.S.G.A. upper weight limit of 1.620 oz.
Other materials may be used in the core composition such as
compatible rubbers or ionomers or low molecular weight fatty acids
such as stearic acid. Free radical initiators such as peroxides may
be added to the core composition so that on the application of heat
and pressure a complex curing crosslinking reaction occurs.
[0037] The golf balls including the core composition of the present
invention can be one-piece, two-piece, or multi-layer balls.
Non-limiting examples of golf balls according to the present
invention include a one-piece ball comprising polybutadiene rubber.
Alternatively, a two-piece ball can be formed with a core formed
from a core composition including polybutadiene rubber of the
present invention and a cover disposed about the core. A
multi-piece ball can also be formed with a core formed from a core
composition including a polybutadiene rubber, a mantle or
intermediate layer, and a cover disposed about the mantle. A
multi-layer ball can also be formed wherein the ball includes a
multi-layer core, where one or more layers of the multi-layer core
is formed from a core composition including polybutadiene rubber in
accordance with the present invention.
[0038] The present invention is also directed to a method for
making a composition exhibiting a particular coefficient of
restitution. The method includes selecting a polybutadiene rubber
exhibiting a particular solution viscosity value. A composition is
then formed including the polybutadiene rubber. The composition
formed exhibits a coefficient of restitution value related to the
solution viscosity value of the polybutadiene rubber. Preferably,
as the solution viscosity of the selected polybutadiene rubber is
higher, the value of the coefficient of restitution for the molded
core formed from the polybutadiene rubber is higher. The Mooney
viscosity of the polybutadiene rubber exhibits a relatively
constant value, preferably from about 38 to about 52, more
preferably 45.+-.5.
[0039] The present invention also relates to a method for making a
golf ball core exhibiting a particular coefficient of restitution.
The method includes selecting a polybutadiene rubber exhibiting a
particular solution viscosity value. A core composition is formed
including the polybutadiene rubber. A core is then formed from the
core composition. The core exhibits a coefficient of restitution
that is related to the solution viscosity of the polybutadiene
rubber. As the solution viscosity value of the polybutadiene rubber
can vary, the Mooney viscosity exhibited by the polybutadiene
rubber remains relatively constant, preferably from about 38 to
about 52, as indicated above.
[0040] The free radical initiator included in the core composition
is any known polymerization initiator (a co-crosslinking agent)
which decomposes during the cure cycle. The term "free radical
initiator" as used herein refers to a chemical which, when added to
a mixture of the elastomeric blend and a metal salt of an
unsaturated, carboxylic acid, promotes crosslinking of the
elastomers by the metal salt of the unsaturated carboxylic acid.
The amount of the selected initiator present is dictated only by
the requirements of catalytic activity as a polymerization
initiator. Suitable initiators include peroxides, persulfates, azo
compounds and hydrazides. Peroxides which are readily commercially
available are conveniently used in the present invention, generally
in amounts of from about 0.1 to about 10.0 and preferably in
amounts of from about 0.3 to about 3.0 parts by weight per each 100
parts of elastomer, wherein the peroxide has a 40% level of active
peroxide.
[0041] Exemplary of suitable peroxides for the purposes of the
present invention are dicumyl peroxide, n-butyl
4,4'-bis(butylperoxy)valerate,
1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane, di-t-butyl
peroxide and 2,5-di-(t-butylperoxy)-2,5 dimethyl hexane and the
like, as well as mixtures thereof. It will be understood that the
total amount of initiators used will vary depending on the specific
end product desired and the particular initiators employed.
Examples of such commercially available peroxides are known in the
art.
[0042] Preferred co-agents which can be used with the above
peroxide polymerization agents include zinc diacrylate, zinc
dimethacrylate, trimethloyl propane triacrylate, and trimethloyl
propane trimethacrylate, most preferably zinc diacrylate. Other
co-agents may also be employed and are known in the art. All of
these co-agents are commercially available.
[0043] The unsaturated carboxylic acid component of the core
composition (a co-crosslinking agent) is the reaction product of
the selected carboxylic acid or acids and an oxide or carbonate of
a metal such as zinc, magnesium, barium, calcium, lithium, sodium,
potassium, cadmium, lead, tin, and the like. Preferably, the oxides
of polyvalent metals such as zinc, magnesium and calcium are used,
and most preferably, the oxide is zinc oxide.
[0044] Exemplary of the unsaturated carboxylic acids which find
utility in the present core compositions are acrylic acid,
methacrylic acid, itaconic acid, crotonic acid, sorbic acid, and
the like, and mixtures thereof. Preferably, the acid component is
either acrylic or methacrylic acid. Usually, from about 15 to about
25, and preferably from about 17 to about 21 parts by weight of the
carboxylic acid salt, such as zinc diacrylate, is included in the
core composition. The unsaturated carboxylic acids and metal salts
thereof are generally soluble in the elastomeric base, or are
readily dispersible.
[0045] Unsaturated polycarboxylic acids which may be employed in
the compositions of the invention include maleic acid, fumaric
acid, itaconic acid and the like, preferably fumaric acid. Use of
fumaric acid in compositions including polybutadiene and epoxy
resins is shown in U.S. Pat. No. 3,671,477.
[0046] In addition to the foregoing, filler materials can be
employed in the compositions of the invention to control the weight
of the ball. Fillers which are incorporated into the compositions
should be in finely divided form, typically in a size generally
less than about 20 mesh, preferably less than about 100 mesh U.S.
standard size. Preferably, the filler is one with a high specific
gravity, such as zinc oxide. Other fillers which may be employed
include, for example, silica, clay, talc, mica, asbestos, glass,
glass fibers, barytes (barium sulfate), limestone, lithophone (zinc
sulphide-barium sulfate), titanium dioxide, zinc sulphide, calcium
metasilicate, silicon carbide, diatomaceous earth, particulate
carbonaceous materials, micro balloons, aramid fibers, particulate
synthetic plastics such as high molecular weight polyethylene,
polystyrene, polyethylene, polypropylene, ionomer resins and the
like, as well as cotton flock, cellulose flock and leather fiber.
Powdered metals such as titanium, tungsten, aluminum, bismuth,
nickel, molybdenum, copper, brass and their alloys also may be used
as fillers. The amount of filler employed is primarily a function
of weight restrictions on the weight of a golf ball made from those
compositions.
[0047] The compositions of the invention also may include various
processing aids known in the rubber and molding arts, such as fatty
acids. Generally, free fatty acids having from about 10 carbon
atoms to about 40 carbon atoms, preferably having from about 15
carbon atoms to about 20 carbon atoms, may be used. Fatty acids
which may be used include stearic acid and linoleic acids, as well
as mixtures thereof. When included in the compositions of the
invention, the fatty acid component is present in amounts of from
about 1 part by weight per 100 parts elastomer, preferably in
amounts of from about 2 parts by weight per 100 parts elastomer to
about 5 parts by weight per 100 parts elastomer. Examples of
processing aids which may be employed include, for example, calcium
stearate, barium stearate, zinc stearate, lead stearate, basic lead
stearate, dibasic lead phosphite, dibutyltin dilaurate, dibutyltin
dimealeate, dibutyltin mercaptide, as well as dioctyltin and
stannane diol derivatives.
[0048] Coloring pigments also may be included in the compositions
of the invention. Useful coloring pigments include, for example,
titanium dioxide, the presence of which simplifies the surface
painting operation of a one piece golf ball. In some cases,
coloring pigments eliminate the need for painting such as, for
example, a one piece golf ball intended for use on driving
ranges.
[0049] The core compositions of the present invention may
additionally contain any other suitable and compatible modifying
ingredients including, but not limited to, metal oxides, fatty
acids, and diisocyanates and polypropylene powder resin.
[0050] Various activators may also be included in the compositions
of the present invention. For example, zinc oxide and/or magnesium
oxide are activators for the polybutadiene. The activator can range
from about 2 to about 50 parts by weight per 100 parts by weight of
the rubbers (phr) component, preferably at least 3 to 5 parts by
weight per 100 parts by weight of the rubbers.
[0051] Higher specific gravity fillers may be added to the core
composition so long as the specific core weight limitations are
met. The amount of additional filler included in the core
composition is primarily dictated by weight restrictions and
preferably is included in amounts of from about 0 to about 100
parts by weight per 100 parts rubber. Ground flash filler may be
incorporated and is preferably mesh ground up center stock from the
excess flash from compression molding. It lowers the cost and may
increase the hardness of the ball.
[0052] Diisocyanates may also be optionally included in the core
compositions. When utilized, the diisocyanates are included in
amounts of from about 0.2 to about 5.0 parts by weight based on 100
parts rubber. Exemplary of suitable diisocyanates is
4,4'-diphenylmethane diisocyanate and other polyfunctional
isocyanates known to the art.
[0053] Furthermore, the dialkyl tin difatty acids set forth in U.S.
Pat. No. 4,844,471, the dispersing agents disclosed in U.S. Pat.
No. 4,838,556, and the dithiocarbamates set forth in U.S. Pat. No.
4,852,884 may also be incorporated into the polybutadiene
compositions of the present invention. The specific types and
amounts of such additives are set forth in the above identified
patents, which are incorporated herein by reference.
[0054] A golf ball formed from compositions of the invention may be
made by conventional mixing and compounding procedures used in the
rubber industry. For example, the ingredients may be intimately
mixed using, for example, two roll mills or a BANBURY.RTM. mixer,
until the composition is uniform, usually over a period of from
about 5 to 20 minutes. The sequence of addition of components is
not critical. A preferred blending sequences is as follows.
[0055] The elastomer, fillers, zinc salt, metal oxide, fatty acid,
and the metallic dithiocarbamate (if desired), surfactant (if
desired), and tin difatty acid (if desired), are blended for about
7 minutes in an internal mixer such as a BANBURY.RTM. mixer. As a
result of shear during mixing, the temperature rises to about
200.degree. F. The initiator and diisocyanate are then added and
the mixing continued until the temperature reaches about
220.degree. F. whereupon the batch is discharged onto a two roll
mill, mixed for about one minute and sheeted out. The mixing is
desirably conducted in such a manner that the composition does not
reach incipient polymerization temperature during the blending of
the various components.
[0056] The composition can be formed into a core structure by any
one of a variety of molding techniques, e.g. injection,
compression, or transfer molding. If the core is compression
molded, the sheet is then rolled into a "pig" and then placed in a
BARWELL.RTM. preformer and slugs are produced. The slugs are then
subjected to compression molding at about 320.degree. F. for about
14 minutes. After molding, the molded cores are cooled at room
temperature for about 4 hours or in cold water for about one
hour.
[0057] Usually the curable component of the composition will be
cured by heating the composition at elevated temperatures on the
order of from about 275.degree. F. to about 350.degree. F.,
preferably and usually from about 290.degree. F. to about
325.degree. F., with molding of the composition effected
simultaneously with the curing thereof. When the composition is
cured by heating, the time required for heating will normally be
short, generally from about 10 to about 20 minutes, depending upon
the particular curing agent used. Those of ordinary skill in the
art relating to free radical curing agents for polymers are
conversant with adjustments to cure times and temperatures required
to effect optimum results with any specific free radical agent.
[0058] After molding, the core is removed from the mold and the
surface may be treated to facilitate adhesion thereof to the
covering materials. Surface treatment can be effected by any of the
several techniques known in the art, such as corona discharge,
ozone treatment, sand blasting, and the like. Preferably, surface
treatment is effected by grinding with an abrasive wheel
(centerless grinding) whereby a thin layer of the molded core is
removed to produce a round core having a diameter of 1.28 to 1.63
inches, preferably about 1.37 to about 1.54 inches, and most
preferably, 1.42 inches. Alternatively, the cores are used in the
as-molded state with no surface treatment.
[0059] One or more cover layers can be applied about the present
core in accordance with procedures known in the art. Any known
cover composition to form a cover can be used. U.S. Pat. Nos.
6,277,921; 6,220,972; 6,150,470; 6,126,559; 6,117,025; 6,100,336;
5,779,562; 5,688,869; 5,591,803; 5,542,677; and 5,368,304, herein
entirely incorporated by reference, disclose cover compositions,
layers, and properties suitable for forming golf balls in
accordance with the present invention.
[0060] When utilized herein, various properties of the balls are
determined as follows:
Coefficient of Restitution
[0061] The coefficient of restitution is the ratio of the outgoing
velocity to the incoming velocity. In the examples of this
application, the coefficient of restitution was measured by
propelling a ball or core horizontally at a speed of 125+/-5 feet
per second (fps) against a generally vertical, hard, flat steel
plate and measuring the ball's incoming and outgoing velocities
electronically. Speeds were measured with a pair of Oehler Mark 55
ballistic screens available from Oehler Research, Inc., Austin,
Tex., which provide a timing pulse when an object passes through
them. The screens were separated by 36 inches and were located
25.25 inches and 61.25 inches from the rebound wall. The ball speed
was measured by timing the pulses from screen 1 to screen 2 on the
way into the rebound wall (as the average speed of the ball over 36
inches), and then the exit speed was timed from screen 2 to screen
1 over the same distance. The rebound wall was tilted 2 degrees
from a vertical plane to allow the ball to rebound slightly
downward in order to miss the edge of the cannon that fired it. The
rebound wall was solid steel 2.0 inches thick.
[0062] The incoming speed should be 125.+-.5 fps but corrected to
125 fps. The correlation between C.O.R. and forward or incoming
speed has been studied and a correction has been made over the
.+-.5 fps range so that the C.O.R. is reported as if the ball had
an incoming speed of exactly 125.0 fps.
Compression
[0063] PGA compression is another important property involved in
the performance of a golf ball. The compression of the ball can
affect the playability of the ball on striking and the sound or
"click" produced. Similarly, compression can effect the "feel" of
the ball (i.e., hard or soft responsive feel), particularly in
chipping and putting.
[0064] Moreover, while compression itself has little bearing on the
distance performance of a ball, compression can affect the
playability of the ball on striking. The degree of compression of a
ball against the club face and the softness of the cover, if
applicable, strongly influence the resultant spin rate. Typically,
a softer cover will produce a higher spin rate than a harder cover.
Additionally, a harder core will produce a higher spin rate than a
softer core. This is because at impact a hard core serves to
compress the cover of the ball against the face of the club to a
much greater degree than a soft core thereby resulting in more
"grab" of the ball on the clubface and subsequent higher spin
rates. In effect the cover is squeezed between the relatively
incompressible core and clubhead. When a softer core is used, the
cover is under much less compressive stress than when a harder core
is used and therefore does not contact the clubface as intimately.
This results in lower spin rates.
[0065] The term "compression" utilized in the golf ball trade
generally defines the overall deflection that a golf ball undergoes
when subjected to a compressive load. For example, PGA compression
indicates the amount of change in a golf ball's shape upon
striking. The development of solid core technology in two-piece
balls has allowed for much more precise control of compression in
comparison to thread wound three-piece balls. This is because in
the manufacture of solid core balls, the amount of deflection or
deformation is precisely controlled by the chemical formula used in
making the cores. This differs from wound three-piece balls wherein
compression is controlled in part by the winding process of the
elastic thread. Thus, two-piece and multilayer solid core balls
exhibit much more consistent compression readings than balls having
wound cores.
[0066] PGA compression relates to a scale of from 0 to 200 given to
a golf ball. The lower the PGA compression value, the softer the
feel of the ball upon striking. In practice, tournament quality
balls have compression ratings around 70 to 110, and preferably
around 80 to 100.
[0067] In determining PGA compression using the 0 to 200 scale, a
standard force is applied to the external surface of the ball. A
ball which exhibits no deflection (0.0 inches in deflection) is
rated 200 and a ball which deflects {fraction (2/10)}th of an inch
(0.2 inches) is rated 0. Every change of 0.001 of an inch in
deflection represents a 1 point drop in compression. Consequently,
a ball which deflects 0.1 inches (100.times.0.001 inches) has a PGA
compression value of 100 (i.e., 200 to 100) and a ball which
deflects 0.110 inches (110.times.0.001 inches) has a PGA
compression of 90 (i.e., 200 to 110).
[0068] An example to determine PGA compression can be shown by
utilizing a golf ball compression tester produced by OK Automation,
Sinking Spring Pa. (formerly Atti Engineering Corporation). The
value obtained by this tester relates to an arbitrary value
expressed by a number which may range from 0 to 100, although a
value of 200 can be measured as indicated by two revolutions of the
dial indicator on the apparatus. The value obtained defines the
deflection that a golf ball undergoes when subjected to compressive
loading. The compression test apparatus consists of a lower movable
platform and an upper movable spring-loaded anvil. The dial
indicator is mounted such that it measures the upward movement of
the springloaded anvil. The golf ball to be tested is placed in the
lower platform, which is then raised a fixed distance. The upper
portion of the golf ball comes in contact with and exerts a
pressure on the springloaded anvil. Depending upon the distance of
the golf ball to be compressed, the upper anvil is forced upward
against the spring.
[0069] Alternative devices have also been employed to determine
compression. For example, Applicant also utilizes a modified Riehle
Compression Machine originally produced by Riehle Bros. Testing
Machine Company, Philadelphia, Pa. to evaluate compression of the
various components (i.e., cores, mantle cover balls, finished
balls, etc.) of the golf balls. The Riehle compression device
determines deformation in thousandths of an inch under a load
designed to emulate the 200 pound spring constant of the other
compression testers. Using such a device, a Riehle compression of
61 corresponds to a deflection under load of 0.061 inches. Other
examples of compression devices include a Whitney Tester or an
Instron.TM.. A set relationship or formula is used to correlate or
correspond to PGA compression.
[0070] Additionally, an approximate relationship between Riehle
compression and PGA compression exists for balls of the same size.
It has been determined by Applicant that Riehle compression
corresponds to PGA compression by the general formula PGA
compression=160-Riehle compression. Consequently, 80 Riehle
compression corresponds to 80 PGA compression, 70 Riehle
compression corresponds to 90 PGA compression, and 60 Riehle
compression corresponds to 100 PGA compression. For reporting
purposes, Applicant's compression values are usually measured as
Riehle compression and converted to PGA compression.
[0071] The present invention is further illustrated by the
following example in which the parts of the specific ingredients
are by weight. It is to be understood that the present invention is
not limited to the example, and various changes and modifications
may be made in the invention without departing from the spirit and
scope thereof.
EXAMPLE
[0072] Core compositions 1-12 were formed from the formulations
shown in Table 4 below. Core compositions 1 and 2 are comparative
core compositions, where core composition 1 is formed from
CARIFLEX.RTM. BR 1220 polybutadiene rubber and core composition 2
is formed from TAKTENE.RTM. 220 polybutadiene rubber.
4 TABLE 4 1 2 3 4 5 6 7 8 9 10 11 12 CARIFLEX .RTM. 100 BR 1220
TAKTENE .RTM. 100 220 BUNA .RTM. CB 100 1405 BUNA .RTM. CB 100 1406
BUNA .RTM. CB 100 1407 BUNA .RTM. CB 100 1409 BUNA .RTM. CB 100
1410 BUNA .RTM. CB 100 1412 BUNA .RTM. CB 100 1414 BUNA .RTM. CB
100 1415 BUNA .RTM. CB 100 1416 BUNA .RTM. CB 100 10 ZnO 22.3 22.3
22.3 22.3 22.3 22.3 22.3 22.3 22.3 22.3 22.3 22.3 T.G. Regrind 20
20 20 20 20 20 20 20 20 20 20 20 Zn Stearate 20 20 20 20 20 20 20
20 20 20 20 20 ZDA 24 24 24 24 24 24 24 24 24 24 24 24 Peroxide
0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90
[0073] Each of the core compositions 1-12 were molded into golf
ball cores and were tested for the particular properties. Table 5
below shows the test results.
5TABLE 5 Sample No. 1 2 3 4 5 6 Size (inches) 1.542 1.542 1.541
1.543 1.543 1.543 Weight (grams) 36.4 36.3 36.3 36.4 36.4 36.5
Compression 88 94 91 90 89 88 (Riehle) C.O.R. .783 .774 .777 .777
.781 .783 Nes Factor.sup.1 871 868 868 867 870 871 Solution
Viscosity 65-70 60 50 60 70 90 mPa .multidot. s MDR s'max torque
81.9 72.2 76.1 77.5 82.1 82.9 Mooney Viscosity .+-.5 40 41 45 45 45
45 Sample No. 7 8 9 10 11 12 Size (inches) 1.543 1.543 1.546 1.543
1.543 1.544 Weight (grams) 36.5 36.4 36.5 36.4 36.4 36.5
Compression 87 88 86 87 85 89 (Riehle) C.O.R. .785 .784 .788 .787
.788 .786 Nes Factor.sup.1 873 872 874 874 873 875 Solution
Viscosity 100 120 140 150 160 140 mPa .multidot. s MDR s'max torque
82.4 81.3 79.9 80.3 80.7 77.4 Mooney Viscosity .+-.5 45 45 45 45 45
45 .sup.1The Nes Factor is the sum of the Riehle Compression and
the C.O.R. (.times.1000). The higher the Nes Factor number, the
higher the resilience.
[0074] The values of the solution viscosity and coefficient of
restitution for each core composition were compared in a graph
shown in FIG. 1. Based on the graph shown in FIG. 1, a relationship
exists between the solution viscosity for each polybutadiene rubber
and the coefficient of restitution for each core. Particularly,
FIG. 1 shows that the greater the value of the solution viscosity
for a polybutadiene rubber, the greater the value of the
coefficient of restitution for the molded core including the
polybutadiene rubber. While a relationship exists between the
solution viscosity value of the polybutadiene rubber and the
coefficient of restitution value of the core, the Mooney viscosity
for the polybutadiene rubber remained at a relatively constant
value.
[0075] It is also shown in FIG. 1 and Table 5 that the controls
(core composition 1, which includes CARIFLEX.RTM. BR 1220
polybutadiene rubber, and core composition 2, which includes
TAKTENE.RTM. 220 polybutadiene rubber), have a lower solution
viscosity and coefficient of restitution when compared to core
compositions 6-12. Core compositions 6-12 each have a solution
viscosity of at least about 90 mPa.s and a coefficient of
restitution of at least about 0.783. Therefore, based upon the
measurement of properties of core compositions 1-12, the greater
the value of the solution viscosity of the polybutadiene rubber,
the greater the value of the coefficient of restitution of the core
composition including the higher solution viscosity polybutadiene
rubber.
[0076] Although the preferred embodiments of the present invention
have been described in detail, various modifications, alterations
and changes or equivalents thereof may be made without departing
from the spirit and scope of the invention.
* * * * *