Note: Descriptions are shown in the official language in which they were submitted.
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GOLF BALL
Cross References to Related Applications
This application is a continuation-in-part application of U.S. Patent
Application Serial No. 09/394,829, filed on September 13, 1999. That
application
is a continuation-in-part of U.S. Patent Application Serial No. 08/870,585,
filed
June 6, 1997, which is a continuation of U.S. Patent Application Serial No.
08/556,237, filed November 9, 1995, which is a continuation-in-part of U.S.
Patent Application Serial No. 08/070,510 filed June 1, 1993. This application
is
also a continuation-in-part application of U.S. Patent Application Serial No.
08/840,392, filed April 29, 1997, now issued as U.S. Patent 5,779,562, which
is
a continuation-in-part of U.S. Patent Application Serial No. 08/631,613, filed
April
10, 1996, which in tum is a continuation-in-part of U.S. Patent Application
Serial
No. 08/591,046, filed on January 25, 1996, and U.S. Patent Application Serial
No. 08/542,793, filed on October 13, 1995, which in turn is a continuation-in-
part
of U.S. Patent Application Serial No. 08/070,510, filed on June 1, 1993. This
~s application also claims priority to U.S. Provisional Application Serial No.
60/171,701, filed December 22, 1999.
Field of the Invention
The present invention relates to golf balls and specifically to the
construction of solid, non-wound, golf balls for regulation play. IVlore
2o particularly, the invention is directed to improved golf balls comprising
multiple
core assemblies which have a comparatively small, high density, polymeric
center, or nucleus, component. The small, heavy center component in
combination with the particular remaining core and cover components
produces a golf ball having a smaller moment of inertia about its central
axis.
2s This results in a golf ball which exhibits enhanced spin while maintaining
or
improving additional golf ball characteristics such as durability, resiliency
and
compression.
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Furthermore, the small, heavy weight, polymeric center
component of the invention is preferably produced without the use of one or
more peroxide crosslinking, or co-crosslinking agents comprising a metal salt
of an unsaturated fatty or carboxylic acid. These crosslinking agents or
coagents are the reaction product of an unsaturated carboxylic acid or acids
and an oxide or carbonate of a metal such as zinc. Examples of such
crosslinking agents, which again are preferably not incorporated into the
present inventions, or if so, only to a minimal amount, include zinc
diacrylate
and zinc dimethacrylate. Accordingly, the polymeric centers of the golf balls
of the present invention are generally free from peroxide crosslinking agents
and exhibit high densities.
Additionally, in a more preferred aspect, the small, heavy center
component of the invention is produced through the use of a blend of
polybutadiene and polyisoprene rubbers. Powdered metal materials and other
materials, including curing agents, may be incorporated therein to produce a
high density, spherical center component that is commercially processible.
Moreover, in a particularly preferred aspect, the balls of the
invention further utilize a multi-layer cover assembly. The improved multi-
layer
cover golf balls provide enhanced distance and durability properties over
single
layer cover golf balls while at the same time offering enhanced "feel" and
spin
characteristics generally associated with soft balata and balata-like covers
of
the prior art.
f3ackgiround of the Invention
Golf balls traditionally have been categorized in three different
a5 groups, namely, as one piece balls, multi-piece solid (two or more pieces)
balls,
and wound (three piece) balls. The one piece ball typically is formed from a
solid
mass of moldable material which has been cured to develop the necessary
degree of hardness. It possesses no significant difference in composition be-
tween the interior and exterior of the ball. These balls do not have an
enclosing
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cover. One piece balls are described, for example, in U.S. Patent No.
3,313,545;
U.S. Patent No. 3,373,123; and, U.S. Patent No. 3,384,612.
The wound ball is frequently referred to as a three piece ball since
it is made with a vulcanized rubber thread wound under tension around a solid
s or semisolid center to form a wound core and thereafter enclosed in a single
or
multilayer covering of tough protective material. For many years the wound
ball
satisfied the standards of the U.S.G.A. and was desired by many skilled, low
handicap golfers.
The three piece wound ball typically has a balata cover which is
relatively soft and flexible. Upon impact, it compresses against the surface
of the
club producing high spin. Consequently, the soft and flexible balata covers
along
with the wound cores provide an experienced golfer with the ability to apply a
spin to control the ball in flight in order to produce a draw or a fade or a
backspin
which causes the ball to "bite" or stop abruptly on contact with the green.
15 Moreover, the balata cover produces a soft "feel" to the low handicap
player.
Such playability properties of workability, feel, etc. are particularly
important in
short iron play with low swing speeds and are exploited significantly by high
skilled players.
However, a three piece wound ball also has several disad-
2o vantages. For example, a wound ball is relatively difficult to manufacture
due
to the number of production steps required and the careful control which must
be exercised in each stage of manufacture to achieve suitable roundness,
velocity, rebound, "click", "feel", and the like.
Additionally, a soft wound (three piece) ball is not well suited for
2s use by the less skilled and/or high handicap golfer who cannot
intentionally
control the spin of the ball. For example, the unintentional application of
side
spin by a less skilled golfer produces hooking or slicing. The side spin
reduces
the golfer's control over the ball as well as reducing travel distance.
Similarly, despite all the benefits of balata, balata covered balls are
3o easily cut and/or damaged if mishit. Consequently, golf balls produced with
balata or balata containing cover compositions, can exhibit a relatively short
life
spans. As a result of this negative property, balata and its synthetic
substitute,
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trans- polyisoprene, and resin blends, have been essentially replaced as the
cover materials of choice by golf ball manufacturers by materials comprising
ionomeric resins and other elastomers such as polyurethanes.
Conventional multi-piece solid golf balls, on the other hand, include
s a solid resilient core having single or multiple cover layers employing
different
types of material molded on the core. The one piece golf ball and the solid
core
for a multi-piece solid (nonwound) ball frequently are formed from a
combination
of materials such as polybutadiene and other rubbers cross linked with zinc
diacrylate or zinc dimethacrylate, and containing fillers and curing agents
which
are molded under high pressure and temperature to provide a ball of suitable
hardness and resilience. For multi-piece nonwound golf balls, the cover
typically
contains a substantial quantity of ionomeric resins that impart toughness and
cut
resistance to the covers.
lonomeric resins are generally ionic copolymers of an olefin, such
as ethylene, and a metal salt of a unsaturated carboxylic acid, such as
acrylic
acid, methacrylic acid or malefic acid. Metal ions, such as sodium or zinc,
are
used to neutralize some portion of the acidic group in the copolymer,
resulting
in a thermoplastic elastomer exhibiting enhanced properties, such as
durability,
for golf ball cover construction. However, some of the advantages gained in
2o increased durability have been offset to some degree by decreases in
playability.
This is because, although the ionomeric resins are very durable, they also
tend
to be quite hard when utilized for golf ball cover construction and thus lack
the
degree of softness required to impart the spin necessary to control the ball
in
flight. Since most ionomeric resins are harder than balata, the ionomeric
resin
2s covers do not compress as much against the face of the club upon impact,
thereby producing less spin. In addition, the harder and more durable ionic
resins lack the "feel" characteristic associated with the softer balata
related
covers.
As a result, while there are currently more than fifty (50)
3o commercial grades of ionomers available, both from DuPont and Exxon, with a
wide range of properties which vary according to the type and amount of metal
ions, molecular weight, composition of the base resin (i.e. relative content
of
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ethylene and methacrylic and/or acrylic acid groups) and additive ingredients,
such as reinforcement agents, etc., a great deal of research continues in
order
to develop golf ball cover compositions exhibiting not only the improved
impact
resistance and carrying distance properties produced by the "hard" ionomeric
s resins, but also the playability (i.e. "spin", "feel", etc.) characteristics
previously
associated with the "soft" balata covers, properties which are still desired
by the
more skilled golfer.
Moreover, a number of multi-piece solid balls have also been
produced to address the various needs of the golfing populations. The
different
types of material used to formulate the core(s), cover(s), etc. of these balls
dramatically alter the balls' overall characteristics.
In this regard, various structures have been suggested using
multilayer cores and single layer covers wherein the core layers have
different
physical characteristics. For example, U.S. Patent Nos. 4,714,253; 4,863,167
~5 and 5,184,828 relate to three piece solid golf balls having improved
rebound
characteristics in order to increase flight distance. The '253 patent is
directed
towards differences in the hardness of the layers. The '167 patent relates to
a
golf ball having a center portion and an outer layer having a high specific
gravity.
Preferably, the outer layer is harder than the center portion. The '828 patent
2o suggests that the maximum hardness must be located at the interface between
the core and the mantle, and the hardness must then decrease both inwardly
and outwardly.
Similarly, a number of patents for multi-piece solid balls suggest
improving the spin and feel by manipulating the core construction. For
example,
2s U.S. Patent No. 4,625,964 relates to a solid golf ball having a core
diameter not
more than 32 mm, and an outer layer having a specific gravity lower than that
of
the core. In U.S. Patent No. 4,650,193, it is suggested that a curable core
elastomer be treated with a cure altering agent to soften an outer layer of
the
core. U.S. Patent No. 5,002,281 is directed towards a three piece solid golf
ball
3o which has an inner core having a gravity greater than 1.0, but less than or
equal
to that of the outer shell which must be less than 1.3. U.S. Patent Nos.
4,848,707 and 5,072,944 disclose three-piece solid golf balls having center
and
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outer layers of different hardness. Other examples of such dual layer cores
can
be found in, but are not limited to, the followings patents: U.S. 4,781,383;
U.S.
4,858,924; U.S. 5,002,281; U.S. 5,048,838; U.S. 5,104,126; U.S. 5,273,286;
U.S.
5,482,285 and U.S. 5,490,674. It is believed that all of these patents are
directed
s to balls with single cover layers.
Multilayer covers containing one or more ionomeric resins have
also been formulated in an attempt to produce a golf ball having the overall
distance, playability and durability characteristics desired. This was
addressed
in U.S. Patent No. 4,431,193, where a multilayered golf ball cover is
described
as having been produced by initially molding a first cover layer on a
spherical
core and then adding a second cover layer. The first or inner layer is
comprised
of a hard, high flexural modulus resinous material to provide a gain in
coefficient
of restitution while the outer layer is a comparatively soft, low flexural
modulus
resinous material to provide spin and control. The increase in the coefficient
of
~5 restitution provides a ball which serves to attain or approach the maximum
initial
velocity limit of 255 feet per second, as provided by the United States Golf
Association (U.S.G.A.) rules. The relatively soft, low flexural modulus outer
layer
provides for an advantageous "feel" and playing characteristics of a balata
covered golf ball.
2o In various attempts to produce a durable, high spin ionomeric golf
ball, the golfing industry has also blended the hard ionomer resins with a
number
of softer ionomer resins. U.S. Patent Nos. 4,884,814 and 5,120,791 are
directed
to cover compositions containing blends of hard and soft ionomeric resins. The
hard copolymers typically are made from an olefin and an unsaturated
carboxylic
2s acid. The soft copolymers are generally made from an olefin, an unsaturated
carboxylic acid and an acrylate ester. It has been found that golf ball covers
formed from hard-soft ionomer blends tend to become scuffed more readily than
covers made of hard ionomer alone.
Most professional golfers and good amateur golfers desire a golf
3o ball that provides good distance when hit off a driver, control and
stopping ability
on full iron shots, and high spin for short "touch and feel" shots. Many
conventional two piece and thread wound performance golf balls have
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undesirable high spin rates on full shots. The excessive spin on full shots is
a
sacrifice made in order to achieve more spin on the shorter touch shots.
Consequently, it would be desirable to produce a multi-piece golf ball that
exhibited low spin on full iron and wood shots and high spin in the "touch"
and
s "feel" shots which occur with the high lofted irons and wedges around the
green.
In this regard, the multi-piece nonwound balls, while having an
advantage with respect to cut resistance, typically have a cover that is
sufficiently
hard so as to provide low deformation upon impact and a small contact area
between the ball and the club face. This provides a greater degree of
"slipperiness" on the club face and, therefore, less control over the ball and
greater difficulty in stopping the ball on the green when using short irons.
At
least some of these deficiencies are considered to result also from a large
moment of inertia exhibited by the multi-piece balls. Thus, it would be useful
to
develop a ball with a controlled moment of inertia coupled with a soft cover
layer
15 in order to provide the desired backspin when using short irons, but at the
same
time without adversely impacting the desired flight and roll distance of the
ball
when using a driver.
A dual core, dual cover ball is described in U.S. Patent No.
4,919,434. However, the patent emphasizes the hardness characteristics of
2o all layers, particularly the requirement for a soft inner cover layer and a
hard
outer cover layer. With respect to the core, it requires that the layers
should
not differ in hardness by more than 10 percent and should be elastomeric
materials having a specific deformation range under a constant load.
U.S. Patent No. 5,104,126 attempts to concentrate the weight of
2s the golf ball in the center core region by utilizing a metal ball as the
core
component. However, that patent teaches the use of a solid metal ball as the
core component which provides substantially different properties than a
polymeric core. Moreover, that patent also teaches the use of density reducing
filler materials incorporated elsewhere in the golf ball. Although perhaps
3o satisfactory in some respects, in other respects, it is undesirable to add
density
reducing fillers to offset the weight of the center core component.
Additionally,
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it would be desirable to simply avoid the use of density reducing fillers if
possible
as they tend to lower the resilience of the golf ball.
Moreover, golf balls utilized in tournament or competitive play
today are regulated for consistency purposes by the United States Golf
s Association (U.S.G.A.). In this regard, there are five (5) U.S.G.A.
specifications which golf balls must meet under controlled conditions. These
are size, weight, velocity, driver distance and symmetry.
Under the U.S.G.A. specifications, a golf ball can not weigh more
than 1.62 ounces (with no lower limit) and must measure at least 1.68 inches
in diameter (with no upper limit). However, as a result of the openness of the
upper or lower parameters in size and weight, a variety of golf balls can be
made. For example, golf balls are manufactured today by the Applicants
which are slightly larger (i.e., approximately 1.72 inches in diameter) while
meeting the weight, velocity, distance and symmetry specifications set by the
15 U.S.G.A.
Additionally, according to the U.S.G.A., the initial velocity of the
ball must not exceed 250 ft/sec. with a 2% maximum tolerance (i.e., 255
ft/sec.) when struck at a set club head speed on a U.S.G.A. machine.
Furthermore, the overall distance of the ball must not exceed 280 yards with
2o a 6% tolerance (296.8 yards) when hit with a U.S.G.A. specified driver at
160
ft/sec. (clubhead speed) at a 10 degree launch angle as tested by the U.S.G.A.
Lastly, the ball must pass the U.S.G.A. administered symmetry test, i.e., fly
consistency (in distance, trajectory and time of flight) regardless of how the
ball is placed on the tee.
25 While the U.S.G.A. regulates five (5) specifications for the
purposes of maintaining golf ball consistency, alternative characteristics
(i.e.,
spin, feel, durability, distance, sound, visibility, etc.) of the ball are
constantly
being improved upon by golf ball manufacturers. This is accomplished by
altering the type of materials utilized and/or improving construction of the
balls.
3o For example, the proper choice of the materials for the covers) and cores)
are important in achieving certain distance, durability and playability
properties.
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Other important factors controlling golf ball performance include, but are not
limited to, cover thickness and hardness, core stiffness (typically measured
as
compression), ball size and surface configuration.
Accordingly, a wide variety of golf balls have been designed and
s are available to suit an individual player's game. In essence, different
types
of balls have been specifically designed or "tailor made" for high handicap
versus low handicap golfers, men versus women, seniors versus juniors, etc.
Moreover, improved golf balls are continually being produced by golf ball
manufacturers with technological advancements in materials and
manufacturing processes.
Two of the principal properties involved in a golf ball's
performance are resilience and compression. Resilience is generally defined
as the ability of a strained body, by virtue of high yield strength and low
elastic
modulus, to recover its size and form following deformation. Simply stated,
~5 resilience is a measure of energy retained to the energy lost when the ball
is
impacted with the club.
In the field of golf ball production, resilience is determined by the
coefficient of restitution (C.O.R.), the constant "e" which is the ratio of
the
relative velocity of an elastic sphere after direct impact to that before
impact.
2o As a result, the coefficient of restitution ("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.
Resilience (C.O.R.), along with additional factors such as club
head speed, club head mass, angle of trajectory, ball size, density,
2s composition and surface configuration (i.e., dimple pattern and area of
coverage) as well as environmental conditions (i.e., temperature, moisture,
atmospheric pressure, wind, etc.) generally determine the distance a golf 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
3o club and the size, density, composition and resilience (C.O.R.) of the ball
and
other factors. The velocity of the club, the mass of the club and the angle of
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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 U.S.G.A., these are not factors of principal
s 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.), spin and the surface configuration (dimple pattern,
ratio of
land area to dimple area, etc.) of the ball.
The coefficient of restitution (C.O.R.) in solid core balls (i.e.,
molded cores and covers) is a function of the composition of the molded core
and of the 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
~5 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, center and cover of a wound core ball may also consist of one or more
layers.
The coefficient of restitution of a golf ball can be analyzed by
2o determining the ratio of the outgoing velocity to the incoming velocity. In
the
examples of this writing, the coefficient of restitution of a golf ball was
measured by propelling a ball horizontally at a speed of 125 +/- 1 feet per
second (fps) against a generally vertical, hard, flat steel plate and
measuring
the ball's incoming and outgoing velocity electronically. Speeds were
2~ measured with a pair of Oehler Mark 55 ballistic screens (available from
Oehler Research Austin TX), which provide a timing pulse when an object
passes through them. The screens are separated by 36" and are located
25.25" and 61.25" 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
30 (as the average speed of the ball over 36"), and then the exit speed was
timed
from screen 2 to screen 1 over the same distance. The rebound wall was
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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.
As indicated above, the incoming speed should be 125 +/- 1 fps.
Furthermore, the correlation between C.O.R. and forward or incoming speed
has been studied and a correction has been made over the +/- fps range so
that the C.O.R. is reported as if the ball had an incoming speed of exactly
125.0 fps.
The coefficient of restitution 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 discussed 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°F when tested on a U.S.G.A.
machine.
Since the coefficient of restitution of a ball is related to the ball's
initial velocity,
it is highly desirable to produce a ball having sufficiently high coefficient
of
~5 restitution (C.O.R.) to closely approach the U.S.G.A. limit on initial
velocity,
while having an ample amount of softness (i.e., hardness) to produce the
desired degree of playability (i.e., spin, etc.).
Furthermore, as mentioned above, the maximum distance a golf
ball can travel (carry and roll) when tested on a U.S.G.A. driving machine set
2o at a club head speed of 160 feet/second is 296.8 yards. While golf ball
manufacturers design golf balls which closely approach this driver distance
specification, there is no upper limit for how far an individual player can
drive
a ball. Thus, while golf ball manufacturers produced balls having certain
resilience characteristics in order to approach the maximum distance
2s parameter set by the U.S.G.A. under controlled conditions, the overall
distance
produced by a ball in actual play will vary depending on the specific
abilities
of the individual golfer.
The surface configuration of a ball is also an important variable
in affecting a ball's travel distance. The size and shape of the ball's
dimples,
3o as well as the overall dimple pattern and ratio of land area to dimpled
area are
important with respect to the ball's overall carrying distance. In this
regard, the
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dimples provide the lift and decrease the drag for sustaining the ball's
initial
velocity in flight as long as possible. This is done by displacing the air
(i.e.,
displacing the air resistance produced by the ball from the front of the ball
to
the rear) in a uniform manner. Moreover, the shape, size, depth and pattern
s of the dimple affect the ability to sustain a ball's initial velocity.
As indicated above, compression is another property involved in
the overall performance of a golf ball. The compression of a ball will
influence
the sound or "click" produced when the ball is properly hit. Similarly,
compression can effect the "feel" of the ball (i.e., hard or soft responsive
feel),
particularly in chipping and putting.
Moreover, while compression of 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 strongly influences the resultant spin rate.
Typically,
~5 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
2o 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.
The term "compression" utilized in the golf ball trade generally
2s 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 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
3o 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
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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
such as the thread wound three-piece balls.
Additionally, cover hardness and thickness are important in
producing the distance, playability and durability properties of a golf ball.
As
mentioned above, cover hardness directly affects the resilience and thus
distance characteristics of a ball. All things being equal, harder covers
produce higher resilience. This is because soft materials detract from
resilience by absorbing some of the impact energy as the material is
compressed on striking.
However, soft covered balls are generally preferred by the more
skilled golfer because he or she can impact high spin rates that give him or
her better control or workability of the ball. Spin rate is an important golf
ball
characteristic for both the skilled and unskilled golfer. As mentioned, high
spin
rates allow for the more skilled golfer, such as PGA and LPGA professionals
and low handicap players, to maximize control of the golf ball. This is
particularly beneficial to the more skilled golfer when hitting an approach
shot
2o to a green. The ability to intentionally produce "back spin", thereby
stopping
the ball quickly on the green, and/or "side spin" to draw or fade the ball,
substantially improves the golfer's control over the ball. Thus, the more
skilled
golfer generally prefers a golf ball exhibiting high spin rate properties.
In view in part of the above information, a number of one-piece,
2s two-piece (a solid resilient center or core with a molded cover), three-
piece
wound (a liquid or solid center, elastomeric winding about the center, and a
molded cover), and multi-layer solid or wound golf balls have been produced
to address the various needs of golfers exhibiting different skill levels. The
different types of materials utilized to formulate the core(s), cover(s), etc.
of
3o these balls dramatically alter the balls' overall characteristics.
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It would be useful to develop a golf ball exhibiting a high spin rate
at low club head speeds when using short, high lofted irons. Such a ball
would exhibit not only high spin but would also have a combination of softness
and durability which is better than the softness-durability combination of a
golf
s ball cover made from a hard-soft ionomer blend. Furthermore, it would be
beneficial to produce a high spin golf ball that produces enhanced spin
characteristics independent of its specific cover composition alone.
These and other objects and features of the invention will be
apparent from the following summary and description of the invention, the
drawings and from the claims.
Summaryr of the Invention
Accordingly, it is a feature of the present invention to provide a
multi-piece, nonwound, solid golf ball. The core is of a multilayer
construction
consisting of two or more polymeric components. The characteristics of the
1s polymeric components of the core are such that the moment of inertia may be
adjusted to enhance the backspin of the ball when using short irons.
An additional feature of the invention is to provide a ball having a
multilayer polymeric core enclosed by a multi-layer cover. The ball has an
appro-
priate moment of inertia that will permit extended flight distance of the ball
and
2o good roll when using a driver, coupled with a cover having sufficient
softness that
will permit deformation of the ball upon impact, thereby increasing the
contact
area between the ball and the club face without subjecting the cover to
undesirable cutting or abrasion.
Another feature of the present invention is the provision for a golf
2s ball of the type described that comprises both multilayer cores and covers)
in
such a manner as to incorporate the desirable features associated with various
categories of balls traditionally employed.
A further feature of the present invention is the provision for a golf
ball core structure with an inner or center polymeric core and an outer
polymeric
3o core layer, with the inner core having a specific gravity that differs from
that of
the outer core layer by more than 2.0, preferably more than 3.0, and most
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preferably more than 6.0, thereby giving the golf ball a moment of inertia
differing
from that of typical solid core balls.
Yet another feature is the provision for a multilayer core that is
combined with a multilayer cover wherein the outer cover layer has a lower
hardness value than the inner cover layer.
A still further feature of the invention is the provision for a golf ball
having a soft outer cover layer with good scuff resistance and cut resistance
coupled with relatively high spin rates at low club head speeds.
The present invention provides in an additional aspect, a solid,
nonwound golf ball, and comprising a multi-core assembly that is
concentrically
positioned within the center of the golf ball, and a multi-layer cover
assembly
disposed about the multi-core assembly. The mass and position of both the
multi-core assembly and the multi-layer cover assembly are such that the
moment of inertia of the golf ball is less than 0.45 oz. in2, preferably less
than
0.44 oz. in2, and more preferably, less than 0.43 oz. in2 for a 1.680" golf
ball.
In yet another aspect, the present invention provides a golf ball
comprising a center core component which is concentrically disposed about a
reference point located at the geometric center of the golf ball. The golf
ball
further comprises an outer core layer which generally surrounds and is
disposed
2o about the center core component. The golf ball further comprises a first
inner
cover layer disposed and positioned around the outer core layer, and a second
outermost dimpled cover layer that is disposed about the first inner cover
layer.
Preferably, an ionomeric material is used in at least one of the cover layers.
The
configuration of the golf ball is such that it has a moment of inertia is
preferably
less than 0.43 oz. inz for a 1.680" golf ball.
In yet another aspect, the present invention provides a golf ball
comprising a center polymeric core component having a specific gravity in the
range of from about 1.2 to about 20, preferably about 2.0 to about 18.0, and a
diameter in the range from about 5 mm to about 21 mm, preferably less than 10
3o mm. The golf ball further comprises an outer core polymeric layer disposed
about the center core layer component, the outer core layer having a specific
gravity in the range from about 0.9 to about 1.2, and an outer diameter in the
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range from about 30 mm to about 40 mm. The golf ball further includes an
inner cover layer disposed about the core layer, and an outer cover layer
disposed about the inner cover layer. The golf ball more preferably exhibits
a moment of inertia of less than 0.43 oz. in2, and a coefficient of
restitution of
at least 0.760, preferably at least 0.780, and most preferably at least 0.800.
In a still further aspect, the present invention relates to a multiple
core component, non-wound, golf ball having small, high density, spherical
center which overcomes the above-referenced problems and others. In this
regard, a smaller (i.e., a diameter of from about 5 mm. to about 21 mm) and
heavier spherical center or center core layer is produced using a blend
composed of a first polymer matrix material comprising a mix of polybutadiene
and polyisoprene rubbers and metal particles, or other high specific gravity
filler
materials: The blend is preferably devoid of any metal carboxylate cross-
linking
or co-crosslinking agents generally present in solid core golf ball
production.
~s In this respect, the high density center is encapsulated by one or
more outer core layers and a cover assembly comprising one or more layers.
The outer core layers) comprise a second polymer matrix material. The size
and weight of the outer core layers) comprising a second polymeric matrix
material and/or cover layers are adjusted in order to produce an overall golf
ball
2o which meets, or is less than, the 1.62 ounce maximum weight limitation
specified
bythe U.S.G.A.
It has been found that the combination of the present invention
produces a golf ball with a decreased moment of inertia and/or a lower radius
of
gyration. This results in the generation of higher spin without substantially
2s affecting the resiliency of the ball. Additionally, the golf ball of the
present
invention exhibits a substantially similar or enhanced feel (i.e., softer
compression) and overall durability.
In an additional aspect, the claimed subject matter of the present
invention provides a golf ball comprising a dual polymeric core and a cover.
so The dual core has an inner, high density, spherical center core layer and
at
least one outer core layer. The high density, spherical center comprises a
blend of high density powdered metal and/or other heavy weight filler
materials
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and a first polymer matrix material selected from thermosets, thermoplastics,
and combinations thereof. Preferably, the first polymer matrix material
comprises a blend of about 90 to about 10 weight percent polybutadiene and
of about 10 to about 90 weight percent polyisoprene. More preferably, the
first polymer matrix material comprises of a blend of about 70 to about 30
weight percent polybutadiene and from about 30 to about 70 weight percent
polyisoprene.
Moreover, in this aspect, the inner, high density, center core layer
is preferably produced without the use of metal carboxylic crosslinking agents
that are generally utilized in solid golf ball core production. These
crosslinking
agents are the reaction product of an unsaturated carboxylic acid or fatty
acids
and an oxide or carbonate of a metal such as zinc. Included are metal salts
of unsaturated fatty acids, for example zinc, aluminum, and calcium salts of
unsaturated fatty acids having 3 to 8 carbon atoms, such as acrylic acid and
methacrylic acid.
The size and weight of the center of this aspect is configured in
a manner to produce a low moment of inertia and a reduced rate of gyration.
For example, the inner spherical center core layer has a specific gravity of
greater than 1.2, preferably greater than 4.0, and most preferably greater
than
7Ø
A lower density outer core layer is disposed about the high
density spherical center core layer. The outer core layer comprises a second
polymer matrix material selected from thermosets, thermoplastics, and
combinations thereof. The second and first polymer matrix materials can be
of the same or different compositions. A cover is then molded about the dual
core.
In a still additional aspect, the present invention is directed to an
improved dual core golf ball having a relatively small, high density spherical
center or nucleus containing powdered tungsten (or other high density
3o powdered metals) in a first elastomeric matrix, such as a blend of
polybutadiene and polyisoprene. The powdered metal elastomeric matrix is
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peroxide, sulfur or radiation crosslinked. Preferably no zinc diacrylate
(ZDA),
zinc dimethyl acrylate (ZDMA) or other unsaturated carboxylic cross-linking
agents are included in the inner spherical center.
One or more outer core layers are disposed about the high
density center, followed by one or more cover layers. The outer core and/or
cover layers are made lighter and/or thicker in order to produce an overall
golf
ball which conforms with the weight and size requirements of the U.S.G.A.
This combination of weight and size displacement decreases the moment of
inertia and/or allows the radius of gyration of the ball to move closer to the
center.
The solid, non-wound, golf balls of the invention will have a
moment of inertia of less than 0.45 oz.in2, preferably less than 0.44 oz.in
for
a standard size golf ball. More preferably the moment of inertia is less than
0.43 oz.in2 for a 1.680" diameter golf ball. The moment of inertia for
oversized
1s or enlarged golf balls, such as balls 1.70 - 1.72 inches in diameter, is
also
reduced.
The moment of inertia (i.e., "M01") of a golf ball (also known as
"rotational inertia") is the sum of the products formed by multiplying the
mass
(or sometimes the area) of each element of a figure by the square of its
2o distance from a specified line such as the center of a golf ball. This
property
is directly related to the "radius of gyration" of a golf ball which is the
square
root of the ratio of the moment of inertia of a golf ball about a given axis
to its
mass. It has been found that the lower the moment of inertia (or the closer
the
radius of gyration is to the center of the ball) the higher the spin rate is
of the
2s ball with all other properties being held equally.
In all of the above aspects, the present invention is directed, in
part, to decreasing the moment of inertia of a solid, non-wound, golf ball by
varying the weight arrangement and composition of the core (preferably the
inner spherical center core layer and the outer core layer). By varying the
3o weight, size and density of the components of the golf ball, the moment of
inertia of a golf ball can be decreased. Additionally, different types of
matrix
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materials and/or crosslinking agents, or lack thereof, can be utilized in the
core
construction in order to produce an overall solid, non-wound, golf ball
exhibiting enhanced spin and feel while maintaining resiliency and durability.
In one other further aspect, the claimed subject matter of the
present application provides a multi-layered covered golf ball comprising a
dual
core and a multi-layer cover. Again, the dual core comprises an inner high
density spherical center core layer and at least one outer core layer. The
inner spherical center comprises a blend of high density powdered metal and/or
other high density material and a first matrix material selected from about a
fifty
1o percent / fifty percent blend of polybutadiene and polyisoprene. The
spherical
center has a specific gravity of greater than 1.2, such as from about 2.0 to
about
20.0, preferably about 4.0 to 18.0, and most preferably, about 7.6 - 7.8 for a
0.340" - 0.344" (8.6-8.75 mm) center.
At least one outer core layer of lower density is disposed about the
~5 inner spherical center. The outer core layer comprises a second matrix
material
selected from thermosets, thermoplastics, and combinations thereof.
The golf ball of this aspect also comprises a multi-layer cover
having at least an inner cover layer and outer cover layer. The inner cover
layer
is disposed about the outer core layer. The outer cover layer is disposed
about
2o and generally surrounds the inner cover layer. One or more intermediate
layers
may also be included.
The golf balls of the present inventions having a high density
elastomeric nucleus, are more durable and softer than solid metal nucleus
balls
while increasing resiliency. The diameter of the center, or nucleus, is
dependant
25 upon the specific gravity of the chosen heavy weight filler and the first
matrix
material so that the maximum U.S.G.A. golf ball weight is not exceeded. The
diameter range of the inner center or nucleus is from about 0.200" (about 5
mm)
to a maximum of about 0.830" (21 mm), more preferably from about 0.300" (about
7.6 mm) to about 0.380" (about 9.65 mm). The most preferred diameter is
30 11/32", or 0.340" to 0.344".
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The density of the most preferred 0.340" to 0.344" center is less
than about 20 grams/cc, preferably less than 12 grams/cc and most preferably
less than 8 grams/cc. The density is set so that it will not exceed the
U.S.G.A.
golf ball weight requirement. These and other objects and features of the
invention will be apparent from the following description and from the claims.
Brief Description of the Drawings
The following is a brief description of the drawings which are
presented for the purposes of illustrating the invention and not for the
purposes
of limiting the same.
FIGURE 1 is a cross-sectional view of a golf ball in accordance
with the present invention comprising a dual core component having a
relatively small, high density spherical center comprising a powdered metal or
other high density filler material dispersed in a first matrix material
comprising
polybutadiene and polyisoprene rubbers, a relatively thick outer core layer
~5 comprising a second matrix material selected from thermosets,
thermoplastics,
or a combination thereof, and a single-layered cover; and
FIGURE 2 is a cross-sectional view of yet another embodiment
golf ball in accordance with the present invention comprising a dual core
component having a relatively small, high density spherical center comprising
2o a powdered metal or other high density filler material dispersed in a first
matrix
material comprising polybutadiene and polyisoprene synthetic rubbers, a
relatively thick outer core layer comprising a second matrix material selected
from thermosets, thermoplastics, or a combination thereof, an inner cover
layer
and an outer cover layer.
2s Detailed Description of the
Preferred Embodiments
The present invention is directed to improved solid, non-wound,
golf balls comprising a polymeric core component with a high density center,
or nucleus, and one or more outer core layers and a polymeric cover
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component with either a single or multi-layer cover. The golf balls of the
present invention can be of standard or enlarged size. The balls possess a
desired combination of properties, including a high coefficient of restitution
(C.O.R.), a low moment of inertia, good sound (click) and feel, and a high
spin
rate on short iron shots.
In this regard, the moment of inertia, sometimes designated "M01"
herein, for the golf balls of the present invention is defined as the sum of
the
products formed by multiplying the mass of each element by the square of its
distance from a specified line or point. This is also known as rotational
inertia.
Since the present invention golf balls comprise a number of components, the
MOI of the resulting golf ball is equal to the sum of the moments of inertia
of
each of its various components, taken about the same axis or point. All of the
moments of inertia of golf balls referred to herein are with respect to, or
are
taken with regard to, the geometric center of the golf ball.
The term or designation "2 x 2" or "2 x 2 construction" as used
herein refers to a golf ball construction utilizing two central core
components,
e.g. a central core component and a core layer disposed about the core
component, and two cover components, e.g. a first inner cover layer and a
second outer cover layer: The present invention however is not limited to 2
2o x 2 configurations and includes 2 x 1 (two core components and a single
cover
component), 3 x 2 (three core components and two cover components), 2 x 3
configurations (two core components and three cover components), 3 x 3
configurations (three core components and three cover components), and
additional configurations such as 4 x 2, 4 x 3, 4 x 4, 2 x 4, 3 x 4, ...etc.
The term "density reducing filler" as used herein refers to
materials having relatively low densities, i.e. that are lightweight or have a
specific gravity less than the specific gravity of the base polybutadiene
rubber
of 0.91. Examples of these materials include lightweight filler materials
typically used to reduce the weight of a product in which they are
incorporated.
3o Specific examples include, for instance, foams and other materials having a
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relatively large void volume. Typically, such filler materials have specific
gravities less than 1Ø
The golf balls of the present invention utilize a unique dual or
multi-component core configuration. Preferably, the core comprises (i) an
s interior spherical center component formed from a blend including a high
density filler material and a first matrix material comprising polybutadiene
and
polyisoprene and (ii) a core layer disposed about the spherical center
component, the core layer formed from a second matrix material such as a
thermoset material, a thermoplastic material, or combinations thereof. The
cores may further comprise (iii) an optional outer core layer disposed about
the
core layer. The outer core layer may be formed from a third matrix material
such as a thermoset material, a thermoplastic material, or combinations
thereof. The first, second or third matrix materials can be of the same or
different materials.
15 The high density center has a specific gravity of greater than 1.2
to about 20.0, and preferably about 4.0 to 18.0, most preferably, 7.6 - 7.8
for
a 0.340" to 0.344" center. The weight of the remaining components are
adjusted so that the ball will not exceed the U.S.G.A. golf ball weight
requirement.
2o In this regard, the present invention is directed to golf balls
comprising a dual core component having a small, high density spherical center
comprising a powdered heavy metal filler or other high density filler
material.
These fillers have a specific gravity of 2.7 or more, preferably 7-8 or more,
and
most preferably 19.35. The high density filler is dispersed in a first matrix
25 material selected from thermosets, thermoplastics, and combinations
thereof.
Preferably, the blend of the high density metal filler materials and
the first matrix material fails to contain any metal carboxylate cross-linking
agents
(i.e., metal salts of unsaturated fatty acids) such as zinc diacrylate (ZDA)
or zinc
dimethyl acrylate (ZDMA).
3o A thick outer core layer is then disposed about the spherical center.
The outer core layer comprises a second matrix material selected from
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thermosets, thermoplastics, and combinations thereof. The outer diameter of
the core is from about 1.25" to 1.60", and most preferably, 1.47" to 1.56". A
cover comprising one or more layers is subsequently molded about the dual core
component to form a solid, non-wound golf ball.
s In a particularly preferred form of the present invention, the golf
ball comprises a dual core assembly that includes a relatively small but heavy
spherical center component, a thick but light core layer disposed about the
spherical center component, and a cover assembly disposed about the dual
core assembly. The heavy center of the core comprises (i) a polymeric
material selected from one or more thermoset materials, thermoplastic
materials or combinations thereof, and (ii) one or more heavy weight powdered
metals having a specific gravity of 2.7 or more dispersed throughout the
polymeric material. Preferably, the heavy center core is comprised of a blend
of polybutadiene and polyisoprene.
~5 The cover assembly may include a single cover or a multi-layered
cover configuration. Preferably, the novel multi-layer golf ball covers of the
present invention include a first or inner layer or ply of a high acid
(greater than
16 weight percent acid) ionomer blend or a low acid (16 weight percent acid or
less) ionomer blend and second or outer layer or ply comprised of a
2o comparatively softer, low modulus ionomer, ionomer blend or other non
ionomeric thermoplastic or thermosetting elastomer such as polyurethane or
polyester elastomer. Most preferably, the inner layer or ply includes a blend
of
low and/or high acid ionomers and has a Shore D hardness of 58 or greater and
the outer cover layer comprised of ionomer or polyurethane and has a Shore D
2s hardness of at least 1 point softer than the inner layer.
Although the present invention is primarily directed to solid, non-
wound, golf balls comprising a dual core component and a multi-layer cover
as described herein, the present invention also includes golf balls having a
dual core component and conventional covers comprising ionomer, balata,
3o various thermoplastic polyurethanes, cast polyurethanes, or any other cover
materials capable of being crosslinked via radiation after cover molding.
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Accordingly, the present invention is directed to golf balls having
a dual-core configuration and a single or multi-layer cover which produces,
upon molding each layer around a high density inner center, a golf ball
exhibiting enhanced spin and feel (i.e., lower compression) without adversely
affecting the ball's resiliency (i.e., distance) and/or durability (i.e., cut
resistance, scuff resistance, etc.) characteristics.
Figures 1 and 2 illustrate preferred embodiments of the golf balls
in accordance with the present invention. It will be understood that all of
the
figures referenced herein are schematic in nature and none of the referenced
figures are to scale. And so, the thicknesses and proportions of the various
layers and the diameter of the various core components are not necessarily
as depicted.
The golf ball 8 comprises a single layer 11 (Figure 1 ) or a multi-
layered cover 12 (Figure 2) disposed about a core 10. The core 10 of the golf
~5 ball is formed (Figure 2) of a small, high density spherical or center core
layer
center 20 and a thick, low density outer core layer 22. The high density
spherical center 20 is designed to produce a low moment of inertia. This
results, in part, in higher spin.
The multi-layered cover 12 (Figure 2) comprises two layers: a
20 first or inner layer or ply 14 and a second or outer layer or ply 16. The
inner
layer 14 can be ionomer, ionomer blends, non-ionomer, non-ionomer blends,
or blends of ionomer and non-ionomer. The outer layer 16 is softer than the
inner layer and can be ionomer, ionomer blends, non-ionomer, non-ionomer
blends or blends of ionomer and non-ionomer.
25 In a first multi-layered cover embodiment, the inner layer 14 is
comprised of a high acid (i.e. greater than 16 weight percent acid) ionomer
resin or high acid ionomer blend. Preferably, the inner layer is comprised of
a blend of two or more high acid (i.e., at least 16 weight percent acid)
ionomer
resins neutralized to various extents by different metal cations. The inner
3o cover layer may or may not include a metal stearate (e.g., zinc stearate)
or
other metal fatty acid salt. The purpose of the metal stearate or other metal
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fatty acid salt is to lower the cost of production without affecting the
overall
performance of the finished golf ball.
In a second multi-layered cover embodiment, the inner layer 14
is comprised of a low acid (i.e., 16 weight percent acid or less) ionomer
blend.
s Preferably, the inner layer is comprised of a blend of two or more low acid
(i.e., 16 weight percent acid or less) ionomer resins neutralized to various
extents by different metal cations. The inner cover layer may or may not
include a metal stearate (e.g., zinc stearate) or other metal fatty acid salt.
It has been found that a hard inner layer in the multi-cover
embodiment provides for a substantial increase in resilience (i.e., enhanced
distance) over known multi-layer covered balls. The softer outer layer along
with the particular multi-component core of the present invention provides the
desirable "feel" and high spin rate characteristic while maintaining the golf
ball's resiliency. The soft outer layer allows the cover to deform more during
~s impact and increases the area of contact between the club face and the
cover,
thereby imparting more spin on the ball. As a result, the soft cover provides
the ball with a balata-like feel and playability characteristics with improved
distance and durability.
Consequently, the overall combination of the high density inner
2o center, one or more outer core layers and the inner and outer cover layers
results in a golf ball having enhanced resilience (improved travel distance)
and
durability (i.e., cut resistance, etc.) characteristics while maintaining, and
in
some instances, improving the playability properties of the ball.
The specific components and characteristics of the solid, non-
25 wound golf balls of the present invention are more particularly set forth
below.
Core Assembly
As noted, the present invention golf balls utilize a unique dual core
configuration. Preferably, the cores comprise (i) an interior, high density,
spherical center or center core layer component formed from a first matrix
3o material comprised of thermoset material, thermoplastic material, or
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combinations thereof and (ii) an outer core layer disposed about the spherical
center component, the core layer being formed from a second matrix material
comprised of thermoset material, thermoplastic material, or combinations
thereof.
Preferably the first matrix material is a blend of polybutadiene and
polyisoprene.
s The spherical center component further comprises a blend of one
or more heavy weight metals and/or filler materials preferably iri particulate
or
powder form, dispersed throughout the thermoset or thermoplastic material.
Preferably, the blend is devoid of any metal carboxylate cross-linking agents.
The outer core layer is disposed immediately adjacent to, and in
intimate contact with the center component. Specifically, one or more outer
core
layers) is disposed about the center core layer. Most preferably, the outer
core
layers) is disposed immediately adjacent to, and in intimate contact with, the
inner core layer(s). The matrix material of the spherical center and the core
layers may be of similar or different composition.
15 The core layers of the golf balls of the present invention generally
are more resilient than that of the cover layers, exhibiting a PGA compression
of
about 85 or less, preferably about 30 to 85, and more preferably about 40-60.
The core compositions and resulting molded core layers of the
present invention are manufactured using relatively conventional techniques.
In
2o this regard, the core compositions of the invention preferably are based on
a
variety of materials, particularly the conventional rubber based materials
such as
cis-1,4 polybutadiene and mixtures of polybutadiene with other elastomers
blended together with crosslinking agents, a free radical initiator, specific
gravity
controlling fillers and the like. However, the use of metal carboxylate
crosslinking
25 agents are preferably not included in the center sphere core layer.
Natural rubber, isoprene rubber, EPR, EPDM, styrene-butadiene
rubber, or similar thermoset materials may be appropriately incorporated into
the
base rubber composition of the butadiene rubber to form the rubber component.
It is preferred to use butadiene rubber as a base material of the composition
for
3o both the central core layer and the outer core layer. Thus, the same rubber
composition, including the rubber base, free radical initiator, and modifying
ingredients, except for the specific gravity controlling filler and
crosslinking agent,
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can be used in both the central and outer core layers. However, different
compositions can readily be used in the different layers, including
thermoplastic
materials such as a thermoplastic elastomer or a thermoplastic rubber, or a
thermoset rubber or thermoset elastomer material.
s Some examples of materials suitable for use as an outer core layer
include the above materials as well as polyether or polyester thermoplastic
urethanes, thermoset polyurethanes or metallocene polymers or blends thereof.
For example, suitable metallocene polymers include foams of thermoplastic
elastomers based on metallocene single site catalyst based foams. Such
1o metallocene based foam resins are commercially available and are readily
suitable for forming the outer core layer.
Examples of a thermoset material include a rubber based, castable
urethane or a silicone rubber. The silicone elastomer may be any thermoset or
thermoplastic polymer comprising, at least partially, a silicone backbone.
15 Preferably, the polymer is thermoset and is produced by intermolecular
condensation of silanols. A typical example is a polydimethylsiloxane
crosslinked
by free radical initiators, or by the crosslinking of vinyl or allyl groups
attached to
the silicone through reaction with silyihydride groups, or via reactive end
groups.
The silicone may include a reinforcing or non-reinforcing filler.
Additionally, the
2o present invention also contemplates the use of a polymeric foam material,
such
as the metallocene based foamed resin for the outer core layers.
More particularly, a wide array of thermoset materials can be
utilized in the core components of the present invention. Examples of suitable
thermoset materials include polybutadiene, polyisoprene, styrene/butadiene,
25 ethylene propylene diene terpolymers, natural rubber polyolefins,
polyurethanes,
silicones, polyureas, or virtually any irreversibly cross-linkable resin
system. It
is also contemplated that epoxy, phenolic, and an array of unsaturated
polyester
resins could be utilized.
The thermoplastic material utilized in the present invention golf
3o balls and, particularly their dual cores, may be nearly any thermoplastic
material.
Examples of typical thermoplastic materials for incorporation in the golf
balls of
the present invention include, but are not limited to, ionomers, polyurethane
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thermoplastic elastomers, and combinations thereof. It is also contemplated
that
a wide array of other thermoplastic materials could be utilized, such as
polysulfones, polyamide-imides, polyarylates, polyaryletherketones, polyaryl
sulfones/polyether sulfones, polyether imides, polyimides, liquid crystal
polymers,
polyphenylene sulfides; and specialty high-performance resins, which would
include fluoropolymers, polybenzimidazole, and ultrahigh molecular weight
polyethylenes.
Additional examples of suitable thermoplastics include
metallocenes, polyvinyl chlorides, polyvinyl acetates, acrylonitrile-butadiene-
styrenes, acrylics, styrene-acrylonitriles, styrene-malefic anhydrides,
polyamides
(nylons), polycarbonates, polybutylene terephthalates, polyethylene
terephthalates, polyphenylene ethers/polyphenylene oxides, reinforced
polypropylenes, and high-impact polystyrenes.
Preferably, the thermoplastic materials have relatively high melting
points, such as a melting point of at least about 300°F. Several
examples of
these preferred thermoplastic materials and which are commercially available
include, but are not limited to, CapronT"~ (a blend of nylon and ionomer),
LexanT""
polycarbonate, Pebax~, and HytreIT"". The polymers or resin system may be
cross-linked by a variety of means such as by peroxide agents, sulphur agents,
2o radiation or other cross-linking techniques, if applicable. However, the
use of
peroxide crosslinking agents is generally preferred in the present invention.
Any or all of the previously described components in the cores of
the golf ball of the present invention may be formed in such a manner, or have
suitable fillers added, so that their resulting density is decreased or
increased.
2s For example, heavy weight metals and/or filler materials are incorporated
into the
inner spherical center. This is discussed in more detail below.
Additionally, the outer core layers are formed or otherwise
produced to be light in weight. For instance, the components could be foamed,
either separately or in-situ. Related to this, a foamed light weight filler
agent or
3o density reducing filler may also be added to the outer core layers.
The specially produced core components of the present invention
are manufactured using relatively conventional techniques. In this regard, the
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preferred core compositions (i.e., center, core layer, outer core layer, etc.)
of
the invention may be based on polybutadiene, and mixtures of polybutadiene
with other elastomers. It is preferred that the base elastomer have a
relatively
high molecular weight. The broad range for the molecular weight of suitable
base elastomers is from about 50,000 to about 500,000. A more preferred
range for the molecular weight of the base elastomer is from about 100,000
to about 500,000. As a base elastomer for the core composition, cis-
polybutadiene is preferably employed, or a blend of cis-polybutadiene with
other elastomers such as polyisoprene may also be utilized. Most preferably,
cis-polybutadiene having a weight-average molecular weight of from about
100,000 to about 500,000 is employed. Along this line, it has been found that
the combination of a high cis-polybutadiene manufactured and sold by Dow
France 13131 Berre I'Etang Cedex, France, tradename Cariflex BR-1220, and
a polyisoprene available from The Goodyear Tire & Rubber Co., Akron, Ohio,
~5 under the designation "NatsynT"" 2200" is particularly well suited.
Although the use of metal carboxylate crosslinking agents is not
preferred for the center core layer, these crosslinkers are included in the
additional outer core layers. The unsaturated carboxylic acid component of the
core composition (a co-crosslinking agent) is the reaction product of the
2o 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 cadmium are used, and most preferably, the oxide is
zinc oxide.
2s 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
12 to about 40, and preferably from about 15 to about 35 parts by weight of
3o the carboxylic acid salt, such as zinc diacrylate, is included in the outer
core
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layers. The unsaturated carboxylic acids and metal salts thereof are generally
soluble in the elastomeric base, or are readily dispersed.
The free radical initiator included in the core compositions is any
known polymerization initiator (a co-crosslinking agent) which decomposes
s 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 0.5 to about 4.0 and preferably in amounts
of from about 1.0 to about 3.0 parts by weight per each 100 parts of elastomer
~5 and based on 40% active peroxide with 60% inert filler.
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
2o 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
LupercoT"" 230 or 231 XL sold by Atochem, Lucidol Division, Buffalo, N.Y., and
TrigonoxT"' 17/40 or 29/40 sold by Akzo Chemie America, Chicago, Illinois.
2s In this regard LupercoT"" 230 XL and TrigonoxT"" 17/40 are comprised of n-
butyl 4,4-bis (butylperoxy) valerate; and, Luperco~"" 231 XL and TrigonoxT""
14/40 are comprised of 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane. The
one hour half life of LupercoT"" 231 XL is about 112°C, and the one
hour half
life of TrigonoxT"" 17/40 is about 129 °C. TrigonoxT"" 42-40 B is
preferred and
3o is chemically tert-Butyl peroxy - 3,5,5, trimethyl hexanoate.
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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. For example, PapiT"" 94, a polymeric diisocyanate, commonly
s available from Dow Chemical Co., Midland, MI., is an optional component in
the rubber compositions. It can range from about 0 to 5 parts by weight per
100 parts by weight rubber (phr) component, and acts as a moisture
scavenger. In addition, it has been found that the addition of a polypropylene
powder resin results in a core which is too hard (i.e. exhibits low
compression)
and thus allows for a reduction in the amount of crosslinking agent utilized
to
soften the core to a normal or below normal compression.
Furthermore, because polypropylene powder resin can be added
to the core composition without an increase in weight of the molded core upon
curing, the addition of the polypropylene powder allows for the addition of
~5 higher specific gravity fillers, such as mineral fillers. Since the
crosslinking
agents utilized in the polybutadiene core compositions are expensive and/or
the higher specific gravity fillers are relatively inexpensive, the addition
of the
polypropylene powder resin substantially lowers the cost of the golf ball
cores
while maintaining, or lowering, weight and compression.
20 The polypropylene (C3H5) powder suitable for use in the present
invention has a specific gravity of about 0.90 g/cm3, a melt flow rate of
about
4 to about 12 and a particle size distribution of greater than 99% through a
20
mesh screen. Examples of such polypropylene powder resins include those
sold by the Amoco Chemical Co., Chicago, Illinois, under the designations
25 "6400 P", "7000 P" and "7200 P". Generally, from 0 to about 25 parts by
weight polypropylene powder per each 100 parts of elastomer are included in
the present invention.
Various activators may also be included in the compositions of
the present invention. For example, zinc oxide, calcium oxide and/or
3o magnesium oxide are activators for the polybutadiene. The activator can
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range from about 2 to about 30 parts by weight per 100 parts by weight of the
rubbers (phr) component.
Fatty acids or metallic salts of fatty acids may also be included
in the compositions, functioning to improve moldability and processing.
Generally, free fatty acids having from about 10 to about 40 carbon atoms, and
preferably having from about 15 to about 20 carbon atoms, are used.
Exemplary of suitable fatty acids are stearic acid and linoleic acids, as well
as
mixtures thereof. Exemplary of suitable metallic salts of fatty acids include
zinc stearate. When included in the core compositions, the fatty acid
1o component is present in amounts of from about 1 to about 25, preferably in
amounts from about 2 to about 15 parts by weight based on 100 parts rubber
(elastomer).
It is preferred that the core compositions include zinc stearate as
the metallic salt of a fatty acid in an amount of from about 2 to about 20
parts
~5 by weight per 100 parts of rubber.
Diisocyanates may also be optionally included in the core
compositions. The diisocyanates act here as moisture scavengers. When
utilized, the diioscyanates are included in amounts of from about 0.2 to about
5.0 parts by weight based on 100 parts rubber. Exemplary of suitable
2o diisocyanates is 4,4'-diphenylmethane diisocyanate and other polyfunctional
isocyanates know to the art.
Furthermore, the dialkyl tin difatty acids set forth in U.S. Patent
No. 4,844,471, the dispersing agents disclosed in U.S. Patent No. 4,838,556,
and the dithiocarbamates set forth in U.S. Patent No. 4,852,884 may also be
25 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.
The preferred core components of the invention are generally
comprised of 100 parts by weight of a base elastomer (or rubber) selected
3o from polybutadiene and mixtures of polybutadiene with other elastomers,
such
as polyisoprene, 12 to 40 parts by weight of at least one metallic salt of an
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unsaturated carboxylic acid, and 0.5 to 4.0 parts by weight of a free radical
initiator (40% active peroxide). However, as mentioned above, the use of at
least one metallic salt of an unsaturated carboxylic acid is preferably not
included in the formulation of the high density center core layer.
In addition to polybutadiene, the following commercially available
thermoplastic resins are also particularly suitable for use in the noted dual
cores
employed in the golf balls of the present invention: CapronT"" 8351 (available
from Allied Signal Plastics), LexanT"" ML5776 (from General Electric), Pebax~
3533 (a polyether block amide from Elf Atochem), and HytreIT"" 64074 (a
polyether ester from DuPont). Properties of these four thermoplastics are set
forth below in Table 1.
TABLE 1
CAPRONT'" 8351
DAM 50%RH ASTM Test
MECHANICAL
Tensile Strength, Yield, psi 7,800 (54) - D-638
(MPa)
Flexural Strength, psi (MPa) 9,500 (65) - D-790
Flexural Modulus, psi (MPa) 230,000 (1,585) D-790
--
Ultimate Elongation, % 200 - D-638
Notched Izod Impact, ft-IbsfinNo Break - D-256
(J/M)
Drop Weight Impact, ft-Ibs 150 (200) - D-3029
(J)
Drop Weight Impact, @ -40F, 150 (200) - D-3029
ft-Ibs (J)
PHYSICAL
Specific Gravity 1.07 - D-792
THERMAL
Melting Point, °F (°C) 420 (215) - D-789
Heat Deflection @ 264 psi °F (°C) 140 (60) - D-648
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LexanT"" ML5776
PROPERTY TYPICAL DATA UNIT METHOD
MECHANICAL
Tensile Strength, yield,8500 psi ASTM D
Type I, 0.125" 638
Tensile Strength, break,9500 psi ASTM D
Type I, 0.125" 638
Tensile Elongation, 110.0 % ASTM D
yield, Type I, 0.125" 638
Flexural Strength, yield,12000 psi ASTM D
0.125" 790
Flexural Modulus, 0.125"310000 psi ASTM D
790
IMPACT
Izod Impact, unnotched,60.0 ft-Ib/in ASTM D
73F 4812
Izod Impact, notched, 15.5 ft-Ib/in ASTM D
73F 256
Izod Impact, notches 12.0 ft-Ibfin ASTM D
73F, 0.250" 256
Instrumented Impact 48.0 fl-Ibs ASTM D
Energy @ Peak, 73F 3763
THERMAL
HDT, 264 psi, 0.250", 257 deg F ASTM D
unannealed 648
Thermal Index, Elec 80 deg C UL 7468
Prop
Thermal Index, Mech 80 deg C UL 7468
Prop with Impact
Thermal Index, Mech 80 deg C UL 7468
Prop without Impact
PHYSICAL
Specific Gravity, solid1.19 - ASTM D
792
Water Absorption, 24 0.150 % ASTM D
hours @ 73F 570
Mold Shrinkage, flow, 5.7 in/in ASTM D
0.125" E-3 955
Melt Flow Rate, nom'I, 7.5 g/10 min ASTM D
300C/l.2kgf(0) 1238
FLAME CHARACTERISTICS
UL File Number, USA E121562 - -
94HB Rated (tested thickness)0.060 inch UL94
PEBAX~ RESINS
ASTM
TEST
PROPERTY METHOD UNITS 3533
Specific Gravity D792
Water Absorption
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Equilibrium 0.5
(20C, 50% R.H.>)
24 Hr. Immersion D570 1.2
Hardness D2240 35D
Tensile Strength, Ultimatepsi 5600
D638
Elongation, Ultimate D638 % 580
Flexural Modulus D790 psi 2800
Izod Impact, Notched D256 ft-
20C Ib.~n. NB
~0C NB
Abrasion Resistance D1044 Mg/1000 104
H 18/1 OOOg Cycles
Tear Resistance Notched D624C Ib.~n. 260
Melting Point D3418 F 306
Vicat Softening Point D1525 F 165
HDT 66 psi D648 F 115
Compression Set
(24 hr., 160F) D395A % 54
HYTRELT'" 64074
2o Thermoplastic Elastomer
PHYSICAL
Dens/Sp Gr ASTM D792 1.1800 sp gr 23/23C
Melt Flow ASTM D12385.20 @E -190 C/2.16 kg g/10/min
Wat Abs ASTM D570 2.100
MECHANICAL
Elong@Brk ASTM D638 230.0%
Flex Mod ASTM D790 9500psi
TnStr@Brk ASTM D638 2000psi
IMPACT
Notch Izod ASTM D256 No Break @ 73.0 F @0.2500
inft-Ib/in
0.50 @ -40.0 F @0.2500 inft-Ib/in
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HARDNESS
Shore ASTM D2240 40 Shore D
THERMAL
DTUL@66 ASTM D648 122 F
Melt Point 338.0 F
Vicat Soft ASTM D1525 248 F
Melt Point
In addition, various polyisoprenes may also be included in the core
components of the present invention. Examples of such polyisoprenes are as
follows:
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TRADENAME ELASTOMER PROPERTIES
Composition Compounding & Processing
Supplier
Isolene Sp. gr. 0.92. Ash, 0.5-1.2%. Volatile matter,
Depolymerized synthetic polyisoprene 0.1 % (24 hour at 300°F), 100%
rubber
Harrlman (flowable form). Grades: Isolene~0 (40,00
cps @ 100°F; Mol wt. mw 40,000); Isolene-
75 viscosity (75,000 cps @ 100°F); DPR-
400 viscosity (400,000 @ 100°F, mol wt.
mw 40,000). Gardner color (60-8)
Natsyn 2200 Sp. gr. 0.91. White, non-staining, solution
Goodyear polymerized, IR with excellent uniformity
R. T. Vanderbilt and purity. Vulcanized with conventional
cure systems, Mooney visc (ml-4 @
212°F). 70-90, needs little or no breakdown.
Tg. 98°F.
Natsyn 2205 Sp. gr. 0.91. White, non-staining, virtually
DuPont gel free solution polymerized IR. Mooney
R. T. Vanderbilt viscosity (ml-4 @ 212°F). 70-90, needs little
or no breakdown. Tg. 98°F.
Natsyn 2210 Sp. gr. 0.91. White, non-staining, low
DuPoni Mooney, solution polymerized, IR with
R. T. Vanderbilt excellent uniformity and purity. Vulcanized
with conventional cure systems, Mooney
visc (ml-4 @ 212°F) 50-65, therefore no
breakdown is required. Tg-98°.
Nipol IR 2200L Sp. gr. 0.92, Mooney visc. ml-4 at 100°C
Goldsmith & Eggleton 70, Cis 1,498%. non-staining.
SKI-3 Staining IR: 97.5 cis 1,4; Mooneyviscosity,
Polyisoprene density 91515.
H.A. Astlett
SKI-3 Mooney visc. MB 1=4 (100°C) 65-85;
Isoprene Rubber Plasticity 0.30-0.41; ultimate elongation,
Nizh USA min. 800; Ultimate tensile strength MPa
(kgF/sq.cm.) min at 23°C 30.4 at 100°C
21.6.
SKI-3 (Russian IR) Staining IR, 97.5 cis 1,4. 60 Mooney
Polyisoprene viscosity, density 91515.
Alcan
SKI-3-S Non-staining 97.5 cis 1,4 73 t 7 Mooney
Polyisoprene viscosity, density 91515.
H.A. Astlett
SKI-3~ (Russian IR) Non-staining 97.5 cis 1,4 73 t 7 Mooney
Polyisoprene viscosity, density 91515.
Alcan
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The inner spherical center preferably can be compression or
transfer molded from an uncured or lightly cured elastomer composition. To
achieve higher coefficients of restitution and/or to increase hardness in the
core,
the manufacturer may include a small amount of a metal oxide such as zinc
oxide. Non-limiting examples of other materials which may be used in the core
composition including compatible rubbers or ionomers, and low molecular weight
fatty acids such as stearic acid. Free radical initiator catalysts such as
peroxides
are admixed with the core composition so that on the application of heat and
pressure, a curing or cross-linking reaction takes place.
Also included in the matrix materials of the inner spherical centers,
are one or more heavy weight fillers or powder materials. Such an inner
spherical center exhibits a lower moment of inertia than conventional two-
piece
golf balls. The moment of inertia for the present golf ball is less than 0.45
oz.in2
and more preferably less than 0.44 oz.in2. Most preferably, the moment of
~5 inertia for the golf ball of the present invention is less than 0.43
oz.in2.
The powdered metal in the spherical center may be in a wide
array of types, geometrics, forms, and sizes. The powdered metal may be of
any shape so long as the metal may be blended with the other components
which form the spherical center.
2o Particularly, the metal may be in the form of metal particles, metal
flakes, and mixtures thereof. However, again, the forms of powdered metal are
not limited to such forms. The metal may be in a form having a variety of
sizes
so long as the objectives of the present invention are maintained. Preferably,
the powdered metal is incorporated into the matrix material of the spherical
2s center in finely defined form, as for example, in a size generally less
than
about 20 mesh, preferably less than about 200 mesh and most preferably less
than about 325 mesh, U.S. standard size. The amount of powdered metal
included in the spherical center is dictated by weight restrictions, the type
of
powdered metal, and the overall characteristics of the finished ball. However,
3o the amount of powdered metal is generally from about 100 to about 3200
parts
by weight matrix material, more preferably, from about 500 to about 1500
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matrix material and most preferably from about 1200 to 1400 matrix material
for a 0.340" diameter polybutadiene center.
The spherical center may include more than one type of
powdered metal. Particularly, the spherical center may include blends of the
s powdered metals disclosed in Table 2 below. The blends of powdered metals
may be in any proportion with respect to each other in order for the spherical
center and golf ball to exhibit the characteristics noted herein.
In this regard, the weight of the inner spherical core component
is increased in the present invention through the inclusion of 100-3200 parts
1o per hundred parts matrix material of metal particles and other heavy weight
filler materials. As used herein, the term "heavy weight filler materials" is
defined as any material having a specific gravity greater than 2.7.
Preferably,
the particles (or flakes, fragments, fibers, etc.) of powdered metal are added
to the inner spherical core in order to decrease the moment of inertia of the
15 ball without affecting the ball's feel and durability characteristics.
The inner spherical core is filled with one or more reinforcing or
non-reinforcing heavy weight fillers such as metal (or metal alloy) powders.
Representatives of such metal (or metal alloy) powders include but are not
limited to, tungsten powder, bismuth powder, boron powder, brass powder,
2o bronze powder, cobalt powder, copper powder, inconnel metal powder, iron
metal powder, molybdenium powder, nickel powder, stainless steel powder,
titanium metal powder, zirconium oxide powder, aluminum flakes, and
aluminum tadpoles.
Examples of several suitable powdered metals which can be
25 included in the present invention are as follows:
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TABLE 2
Metals and Alloys (Powders) Specific Gravity
titanium 4.51
tungsten 19.35
bismuth 9.78
nickel 8.90
molybdenum 10.2
iron 7.86
copper 8.94
brass 8.2-8.4
bronze 8.70-8.74
cobalt 8.92
zinc 7.14
tin 7.31
aluminum 2.70
The amount and type of powdered metal utilized is dependent
upon the overall characteristics of the high spinning, soft feeling, golf ball
desired. Generally, lesser amounts of high specific gravity powdered metals
are necessary to produce a decrease in the moment of inertia in comparison
2o to low specific gravity materials. Furthermore, handling and processing
conditions can also effect the type of heavy weight powdered metals
incorporated into the spherical center. In this regard, Applicants have found
that the inclusion of approximately 1200-1400 phr tungsten powder into the
inner spherical center produces the desired increase in the moment of inertia
without involving substantial processing changes. Thus, 1200-1400 phr
tungsten powder is the most preferred heavy filler material at the time of
this
writing for a 0.340" diameter polybutadiene center or nucleus.
Furthermore, powdered iron can also be preferably blended with
powdered tungsten or other powdered materials in the spherical center so that
3o the spherical center can be attracted to a magnet. The magnetic attraction
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allows for automated assembly of the spherical center to the remaining layers
in forming the golf ball. Preferably, the powdered iron is about 4-10% by
weight
of the spherical center composition when used as an attraction agent for a
magnet.
The powdered metal constitutes at least 50% by weight of the total
spherical center composition. Preferably, the powdered metal constitutes at
least 60% of the spherical center composition. Most preferably, the powdered
metal constitutes at least 70% of the spherical center composition.
When the preferred high density powdered metal comprises the
spherical center, the diameter of the spherical center can vary considerably
so
long as the maximum U.S.G.A. golf ball weight is not exceeded. Preferably,
the spherical center has a diameter in the range of about 0.200 inches to
about 0.830 inches. More preferably, the diameter of the spherical center is
from about 0.200 inches to about 0.400 inches, most preferably from about
~5 0.300 inches to about 0.380 inches, with 0.340 - 0.344 inches being
optimal.
The spherical center comprising a high density powdered metal
has a density that will not exceed the U.S.G.A. golf ball weight requirement.
Preferably, the density is no more than about 12-20, preferably less than 9
grams/cm3 for a 0.340" - 0.344" diameter nucleus.
2o The outer diameter of the center core and the outer diameter of the
outer core (core diameter) may vary. However, the center core has a diameter
of about 5 to 21 mm and preferably about 5 to 15 mm while the outer core has
a diameter of about 30 to 40 mm and preferably 35 to 38 mm, depending on the
size of the center core and the finished size of the ball. Typically the
center core
2s diameter is about 5 to 12 mm.
The core having a two-layer structure composed of the inner core
and the outer core is referred to as the solid core in the present invention.
The
above expression is in contrast to a thread-wound core (core formed by winding
a rubber thread around the center portion which is solid or filled with a
liquid
30 material).
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The double cores of the inventive golf balls typically have a
coefficient of restitution of about 0.730 or more, more preferably 0.770 or
more
and a PGA compression of about 95 or less, and more preferably 70 or less.
The double cores have a weight of 25 to 40 grams and preferably 30 to 40
s grams and a Shore C hardness of less than 80, with the preferred Shore C
hardness being about 50 to 75.
As mentioned above, the present invention includes golf ball
embodiments that utilize two or more core components. For example, in
accordance with the present invention, a core assembly is provided that
comprises a central core component and one or more core layers disposed
about the central core component. Details for the second and third or more
core layers are also included herein in the description of the core layer
utilized
in a dual core configuration.
In producing golf ball centers utilizing the present compositions,
~5 the ingredients may be intimately mixed using, for instance, two roll mills
or a
BanburyT"" mixer until the composition is uniform, usually over a period of
from
about 5 to about 20 minutes. The sequence of addition of components is not
critical. A preferred blending sequence is described below.
The matrix material or elastomer, powdered metal zinc salt (if
2o desired), the high specific gravity additive such as powdered metal, 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 BanburyT"" mixer. As a result of shear during mixing,
the temperature rises to about 200°F. The mixing is desirably conducted
in
25 such a manner that the composition does not reach incipient polymerization
temperatures during the blending of the various components. The initiator and
diisocyanate are then added and the mixing continued until the temperature
reaches about 220°F whereupon the batch is discharged onto a two roll
mill,
mixed for about one minute and sheeted out.
3o The sheet is rolled into a "pig" and then placed in a BarvveIIT""
preformer and slugs of the desired weight are produced. The slugs to be used
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for the center core layer are then subjected to compression molding at about
140°C to about 170°C for about 10 to 50 minutes. Note that the
temperature in
the molding process is not always required to be constant, and may be changed
in two or more steps. In fact, the slugs for the outer core layer are
frequently
s preheated for about one half hour at about 75°C prior to molding.
After molding,
the molded centers are cooled, the cooling effected at room temperature for
about 4 hours or in cold water for about one hour. The molded centers are
subjected to a centerless grinding operation whereby a thin layer of the
molded
core is removed to produce a round center. Alternatively, the centers are used
in the as-molded state with no grinding needed to achieve roundness.
The solid inner centers are generally from 0.200 to 0.830 inches
in diameter, preferably 0.300 to 0.380 inches, and most preferably 0.320 to
0.360 inches, with a weight of 1.2 grams to 5.9 grams, preferably 1.8 to 3.6
grams, and most preferably 2.6 to 3.0 grams for a 0.340" - 0.344" diameter
15 nucleus. The specific gravity of the inner spherical center is from 1.2 to
20.0,
preferably 5 to 12, and most preferably 7.6 to 7.9 for a 0.340" -
0.344'°
diameter nucleus.
The center is converted into a dual core by providing at least one
layer of core material thereon, ranging in thickness from about 0.69 to about
20 0.38 inches and preferably from about 0.65 to about 0.60 inches. The outer
core layers may be of similar or different matrix material as the spherical
center. Preferably the outer core layer comprises polybutadiene which has
been weight adjusted to compensate for the heavy weight spherical center.
The outer core layer can be applied around the spherical center
2s by several different types of molding processes. For example, the
compression molding process for forming the cover layers) of a golf ball that
is set forth in U.S. Patent No. 3,819,795 can be adapted for use in producing
the core layers) of the present invention.
In such a modified process, preforms or slugs of the outer core
3o material, i.e., the thermoset material utilized to form the outer core
layer, are
placed in the upwardly open, bottom cavities of a lower mold member of a
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compression molding assembly, such as a conventional golf ball or core platen
press. The upwardly facing hemispherical cavities have inside diameters
substantially equal to the finished core to be formed. In this regard, the
inside
diameters of the cavities are slightly larger (i.e., approximately 0.010"
diameter)
s than the desired finished core size in order to account for material
shrinkage.
An intermediate mold member comprising a center Teflon~-coated
plate having oppositely-affixed hemispherical protrusions extending upwardly
on
the upper surface and extending downwardly on the lower surface, each
hemispherical protrusion about 0.340 inches in diameter, is placed over the
lower
~o mold member and on top of the preforms located in the bottom molding
cavities.
The size and outside diameters of the hemispherical protrusions are
substantially
equal to the centers to be utilized and thus can vary with the various sizes
of the
centers to be used.
Additional preforms of the same outer core material are
~5 subsequently placed on top of the upperly-projecting 0.340" hemispherical
protrusions affixed to the upper surfaces of the Teflon~-coated plate of the
intermediate mold member. The additional preforms are then covered by the
downwardly open cavities of the top mold member. Again the downward facing
cavities of the top mold member have inside diameters substantially equal to
the
2o core to be formed.
Specifically, the bottom mold member is engaged with the top mold
member with the intermediate mold member having the oppositely protruding
hemispheres being present in the middle of the assembly. The mold members
are then compressed together to form hemispherical core halves.
25 In this regard, the mold assembly is placed in a press and cold
formed at room temperature using approximately 10 tons of pressure in a steam
press. The molding assembly is closed and heated below the cure activation
temperature of about 150°F for approximately four minutes to soften and
mold
the outer core layer materials. While still under compression, but at the end
of
3o the compression cycle, the mold members are water cooled to a temperature
to
less than 100°F in order to maintain material integrity for the final
molding step.
This cooling step is beneficial since cross linking has not yet proceeded to
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provide internal chemical bonds to provide full material integrity. After
cooling,
the pressure is released.
The molding assembly is then opened, the upper and lower mold
members are separated, and the intermediate mold member is removed while
maintaining the formed outer core layer halves in their respective cavities.
Each
of the halves has an essentially perfectly formed one-half shell cavity or
depression in its uncured thermoset material. These one-half shell cavities or
depressions were produced by the hemispherical protrusions of the intermediate
mold member.
Previously molded centers of about 0.340" in diameter, are then
placed into the bottom cavities or depressions of the uncured thermoset
material.
The top portion of the molding assembly is subsequently engaged with the
bottom portion and the material that is disposed therebetween is cured for
about
12 minutes at about 320°F. Those of ordinary skill in the art relating
to free
radical curing agents for polymers are conversant with adjustments of cure
times
and temperatures required to effect optimum results with any specific free
radical
agent. The combination of the high temperature and the compression force joins
the core halves, and bonds the cores to the center. This process results in a
substantially continuously outer core layer being formed around the center
component.
In an alternative, and in some instances, more preferable
compression molding process, the Teflon~-coated plate of the intermediate mold
member has only a set of downwardly projecting hemispherical protrusions and
no oppositely affixed upwardly-projecting hemispherical protrusions.
Substituted
for the upwardly-projecting protrusions are a plurality of hemispherical
recesses
in the upper surface of the plate. Each recess is located in the upper surface
of
the plate opposite a protrusion extending downwardly from the lower surface.
The recess has an inside diameter substantially equal to the center to be
utilized
and is configured to receive the bottom half of the center.
3o The previously molded centers of about 0.340" in diameter are then
placed in the cavities located on the upper surface of the plate of the
intermediate mold member. Each of the centers extends above the upper
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surface of the plate of the intermediate mold member and is pressed into the
lower surface of the upper preform when the molds are initially brought
together
during initial compression.
The molds are then separated and the plate removed, with the
s centers being retained (pressed into) the half shells of the upper preforms.
Mating cavities or depressions are also formed in the half shells of the lower
preforms by the downwardly projecting protrusions of the intermediate mold
member. With the plate now removed, the top portion of the molding assembly
is then joined with the bottom portion. In so doing, the centers projecting
from
1o the half shells of the upper performs enter into the cavities or
depressions formed
in the half shells of the lower preforms. The material included in the molds
is
subsequently compressed, treated and cured as stated above to form a golf ball
core having a centrally located center and an outer core layer. This process
can
continue for additional added core layers.
15 After molding, the core comprising a centrally located center
surrounded by at least one outer core layer is removed from the mold and the
surface thereof preferably is 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
2o blasting, brush tumbling, and the like. Preferably, surface treatment is
effected
by grinding with an abrasive wheel.
COVER ASSEMBLY
A. Multi-Covers
i. Inner Cover Layer
25 The inner cover layer is harder than the outer cover layer and
generally has a thickness in the range of 0.01 to 0.10 inches, preferably 0.03
to 0.07 inches for a 1.68 inch ball and 0.05 to 0.10 inches for a 1.72 inch
(or
more) ball. The core and inner cover layer together form an inner ball having
a coefficient of restitution of 0.780 or more and more preferably 0.790 or
mores
3o and a diameter in the range of 1.48 - 1.64 inches for a 1.68 inch ball and
1.50
- 1.70 inches for a 1.72 inch (or more) ball. The inner cover layer has a
Shore
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D hardness of 60 or more. It is particularly advantageous if the golf balls of
the invention have an inner layer with a Shore D hardness of 65 or more. The
above-described characteristics of the inner cover layer provide an inner ball
having a PGA compression of 100 or less. It is found that when the inner ball
s has a PGA compression of 90 or less, excellent playability results.
The inner layer compositions include the high acid ionomers such
as those developed by E.I. DuPont de Nemours & Company under the
trademark "Surlyn~" and by Exxon Corporation under the trademark "EscorT"""
or trade name "lotek", or blends thereof. Examples of compositions which may
be used as the inner layer herein are set forth in detail in a continuation of
U.S. Application Serial No. 08/174,765, which is a continuation of U.S.
Application Serial No. 07/776,803 filed October 15, 1991, and Serial No.
08/493,089, which is a continuation of 07/981,751, which in turn is a
continuation of Serial No. 07/901,660 filed June 19, 1992, all of which are
~s incorporated herein by reference. Of course, the inner layer high acid
ionomer
compositions are not limited in any way to those compositions set forth in
said
applications.
The high acid ionomers which may be suitable for use in
formulating the inner layer compositions are ionic copolymers which are the
2o metal, i.e., sodium, zinc, magnesium, etc., salts of the reaction product
of an
olefin having from about 2 to 8 carbon atoms and an unsaturated
monocarboxylic acid having from about 3 to 8 carbon atoms. Preferably, the
ionomeric resins are copolymers of ethylene and either acrylic or methacrylic
acid. In some circumstances, an additional comonomer such as an acrylate
2s ester (i.e., iso- or n-butylacrylate, etc.) can also be included to produce
a softer
terpolymer. The carboxylic acid groups of the copolymer are partially
neutralized (i.e., approximately 10-100%, preferably 30-70%) by the metal
ions.
Each of the high acid ionomer resins which may be included in the inner layer
cover compositions of the invention contains greater than about 16% by weight
30 of a carboxylic acid, preferably from about 17% to about 25% by weight of a
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carboxylic acid, more preferably from about 18.5% to about 21.5% by weight
of a carboxylic acid.
Although the inner layer cover composition of several
embodiments of the present invention preferably includes a high acid
s ionomeric resin, the scope of the patent embraces all known high acid
ionomeric resins falling within the parameters set forth above, only a
relatively
limited number of these high acid ionomeric resins have recently become
commercially available.
The high acid ionomeric resins available from Exxon under the
designation "EscorT""" and or "lotek", are somewhat similar to the high acid
ionomeric resins available under the "Surlyn~" trademark. However, since the
EscorT""/lotek ionomeric resins are sodium or zinc salts of polyethylene-
acrylic
acid) and the "Surlyn~" resins are zinc, sodium, magnesium, etc. salts of
polyethylene-methacrylic acid), distinct differences in properties exist.
15 Examples of the high acid methacrylic acid based ionomers found
suitable for use in accordance with this invention include Surlyn~8220 and
8240 (both formerly known as forms of Surlyn~ AD-8422), Surlyn~9220 (zinc
ration), Surlyn~SEP-503-1 (zinc ration), and Surlyn~SEP-503-2 (magnesium
ration). According to DuPont, all of these ionomers contain from about 18.5
2o to about 21.5% by weight methacrylic acid.
More particularly, Surlyn~ AD-8422 is currently commercially
available from DuPont in a number of different grades (i.e., AD-8422-2, AD-
8422-3, AD-8422-5, etc.) based upon differences in melt index. According to
DuPont, Surlyn~ 8422, which is believed recently to have been redesignated
25 as 8220 and 8240, offers the following general properties when compared to
Surlyn~ 8920, the stiffest, hardest of all on the low acid grades (referred to
as
"'hard" ionomers in U.S. Patent No. 4,884,814):
LOW ACID HIGH ACID
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(15 wt% Acid) (>20 wt% Acid)
SURLYN~ SURLYN~ SURLYN~
8920 8422-2 8422-3
IONOMER
Cation Na Na Na
Melt Index 1.2 2.8 1.0
Sodium, Wt% 2.3 1.9 2.4
Base Resin MI 60 60 60
MP', C 88 86 85
1o FP', C 47 48.5 45
COMPRESSION MOLDING2
Tensile Break,
psi 4350 4190 5330
Yield, psi 2880 3670 3590
~5 Elongation, 315 263 289
%
Flex Mod,
K psi 53.2 76.4 88.3
Shore D
hardness 66 67 68
' DSC second heat, 10°C/min heating rate.
Z Samples compression molded at 150°C annealed 24
hours at 60°C. 8422-2, -3 were homogenized at
190°C before molding.
In comparing Surlyn~ 8920 to Surlyn~ 8422-2 and Surlyn~ 8422-
3, it is noted that the high acid Surlyn~ 8422-2 and 8422-3 ionomers have a
higher tensile yield, lower elongation, slightly higher Shore D hardness and
much higher flexural modulus. Surlyn~ 8920 contains 15 weight percent
methacrylic acid and is 59% neutralized with sodium.
3o In addition, Surlyn~SEP-503-1 (zinc cation) and Surlyn~SEP-
503-2 (magnesium cation) are high acid zinc and magnesium versions of the
Surlyn~AD 8422 high acid ionomers. When compared to the Surlyn~ AD
8422 high acid ionomers, the Surlyn~ SEP-503-1 and SEP-503-2 ionomers
can be defined as follows:
Su~rn~ lonomer Ion Melt Index Neutralization
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AD 8422-3 Na 1.0 45
SEP 503-1 Zn 0.8 38
SEP 503-2 Mg 1.8 43
Further, Surlyn~ 8162 is a zinc cation ionomer resin containing
approximately 20% by weight (i.e., 18.5 - 21.5% weight) methacrylic acid
copolymer that has been 30 - 70% neutralized. Surlyn~ 8162 is currently
commercially available from DuPont.
Examples of the high acid acrylic acid based ionomers suitable
for use in the present invention also include the EscorTM or lotek high acid
ethylene acrylic acid ionomers produced by Exxon such as Ex 1001, 1002,
959, 960, 989, 990, 1003, 1004, 993, 994. In this regard, EscorT"" or lotek
959
is a sodium ion neutralized ethylene-acrylic neutralized ethylene-acrylic acid
copolymer. According to Exxon, loteks 959 and 960 contain from about 19.0
to 21.0% by weight acrylic acid with approximately 30 to about 70 percent of
the acid groups neutralized with sodium and zinc ions, respectively. The
physical properties of these high acid acrylic acid based ionomers are set
forth
in Tables 3 and 4 as follows:
TABLE 3
Ph ysical perties of Various
Pro lonomers
ESCORTM ESCORyM
PROPERTY Ex1001 Ex1002 (IOTEK) X1003 Ex1004 (IOTEK)
959 960
Melt index,
g/10 min 1.0 1.6 2.0 1.1 2.0 1.8
Cation Na Na Na Zn Zn Zn
Melting
Point, 183 183 172 180 180.5 174
F
scat
Softening
Point, F 125 125 130 133 131 131
Tensile 34.4 22.5 4600 24.8 20.6 3500
@ Break MPa MPa psi MPa MPa psi
Elongation
Break, % 341 348 325 387 437 430
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Hardness,
Shore D 63 62 66 54 53 57
Flexural 365 380 66,000 147 130 27,000
Modulus MPa MPa psi MPa MPa psi
TABLE
4
Phy rsical perties
Pro of Various
lonomers
EX 989 EX 993 EX 994 EX
990
Melt index g/10 1.30 1.25 1.32 1.24
min
Moisture ppm 482 214 997 654
Cation type - Na Li K Zn
M+ content by wt% 2.74 0.87 4.54 0
AAS
Zn content by wt% 0 0 0 3.16
AAS
Density kg/m' 959 945 976 977
Vicat softening C 52.5 51 50 55.0
point
Crystallization C 40.1 39.8 44.9 54.4
point
'95Melting point C 82.6 81.0 80.4 81.0
Tensile at yield MPa 23.8 24.6 22 16.5
Tensile at break MPa 32.3 31.1 29.7 23.8
Elongation at % 330 260 340 357
break
1% secant modulusMPa 389 379 312 205
Flexural modulus MPa 340 368 303 183
Abrasion resistancemg 20.0 9.2 15.2 20.5
Hardness Shore - 62 62.5 61 56
D
Zwick Rebound % 61 63 59 48
Furthermore, as a result of the development by the assignee of
2s this application of a number of new high acid ionomers neutralized to
various
extents by several different types of metal cations, such as by manganese,
lithium, potassium, calcium and nickel rations, several new high acid ionomers
and/or high acid ionomer blends besides sodium, zinc and magnesium high
acid ionomers or ionomer blends are now available for golf ball cover
3o production. It has been found that these new ration neutralized high acid
ionomer blends produce inner cover layer compositions exhibiting enhanced
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hardness and resilience due to synergies which occur during processing.
Consequently, the metal cation neutralized high acid ionomer resins recently
produced can be blended to produce substantially higher C.O.R.'s than those
produced by the low acid ionomer inner cover compositions presently
s commercially available.
More particularly, several new metal cation neutralized high acid
ionomer resins have been produced by the assignee by neutralizing, to various
extents, high acid copolymers of an alpha-olefin and an alpha, beta-
unsaturated carboxylic acid with a wide variety of different metal cation
salts.
This discovery is the subject matter of U.S. Patent No. 5,688,869,
incorporated
herein by reference. It has been found that numerous new metal cation
neutralized high acid ionomer resins can be obtained by reacting a high acid
copolymer (i.e., a copolymer containing greater than 16% by weight acid,
preferably from about 17 to about 25 weight percent acid, and more preferably
~s about 20 weight percent acid), with a metal cation salt capable of ionizing
or
neutralizing the copolymer to the extent desired (i.e., from about 10% to
90%).
The base copolymer is made up of greater than 16% by weight
of an alpha, beta-unsaturated carboxylic acid and an alpha-olefin. Optionally,
a softening comonomer can be included in the copolymer. Generally, the
2o alpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene, and
the
unsaturated carboxylic acid is a carboxylic acid having from about 3 to 8
carbons. Examples of such acids include acrylic acid, methacrylic acid,
ethacrylic acid, chloroacrylic acid, crotonic acid, malefic acid, fumaric
acid, and
itaconic acid, with acrylic acid being preferred.
2s The softening comonomer that can be optionally included in the
inner cover layer for the golf ball of the invention may be selected from the
group consisting of vinyl esters of aliphatic carboxylic acids wherein the
acids
have 2 to 10 carbon atoms, vinyl ethers wherein the alkyl groups contains 1
to 10 carbon atoms, and alkyl acrylates or methacrylates wherein the alkyl
3o group contains 1 to 10 carbon atoms. Suitable softening comonomers include
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vinyl acetate, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl
methacrylate, butyl acrylate, butyl methacrylate, or the like.
Consequently, examples of a number of copolymers suitable for
use to produce the high acid ionomers included in the present invention
include, but are not limited to, high acid embodiments of an ethylene/acrylic
acid copolymer, an ethylene/methacrylic acid copolymer, an ethylene/itaconic
acid copolymer, an ethylene/maleic acid copolymer, an ethylene/methacrylic
acid/vinyl acetate copolymer, an ethylene/acrylic acid/vinyl alcohol
copolymer,
etc. The base copolymer broadly contains greater than 16% by weight
unsaturated carboxylic acid, from about 39 to about 83% by weight ethylene
and from 0 to about 40% by weight of a softening comonomer. Preferably, the
copolymer contains about 20% by weight unsaturated carboxylic acid and
about 80°/D by weight ethylene. Most preferably, the copolymer contains
about
20% acrylic acid with the remainder being ethylene.
~5 Along these lines, examples of the preferred high acid base
copolymers which fulfill the criteria set forth above, are a series of
ethylene-
acrylic copolymers which are commercially available from The Dow Chemical
Company, Midland, Michigan, under the "PrimacorT""" designation. These high
acid base copolymers exhibit the typical properties set forth below in Table
5.
2o TABLE 5
Tyuical Properties of Primacor
Ethylene-Acryrlic Acid Copolymers
GRADE PERCENT DENSITY, MELT INDEX, TENSILE FLEXURAL VICAT SHORE D
ACID glcc gHOmin YD. ST (psi) MODULUS SOFT PT (°C) HARDNESS
(P$7
ASTM D-792 D-1238 D-638 D-790 D-1525 D-2240
25 5980 20.0 0.958 300.0 - 4800 43 50
5990 20.0 0.955 1300.0 650 2600- 40 42
3200
5981 20.0 0.960 300.0 900 3200 46 48
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5983 20.0 0.958 500.0 850 3100 44 45
5991 20.0 0.953 2600.0 635 2600 38 40
'The Melt Index values are obtained according to ASTM D-1238, at 190°C.
s Due to the high molecular weight of the Primacor 5981 grade of
the ethylene-acrylic acid copolymer, this copolymer is the more preferred
grade
utilized in the invention.
The metal cation salts utilized in the invention are those salts
which provide the metal cations capable of neutralizing, to various extents,
the
carboxylic acid groups of the high acid copolymer. These include acetate,
oxide or hydroxide salts of lithium, calcium, zinc, sodium, potassium, nickel,
magnesium, and manganese.
Examples of such lithium ion sources are lithium hydroxide
monohydrate, lithium hydroxide, lithium oxide and lithium acetate. Sources for
~5 the calcium ion include calcium hydroxide, calcium acetate and calcium
oxide.
suitable zinc ion sources are zinc acetate dihydrate and zinc acetate, a blend
of zinc oxide and acetic acid. Examples of sodium ion sources are sodium
hydroxide and sodium acetate. Sources for the potassium ion include
potassium hydroxide and potassium acetate. Suitable nickel ion sources are
2o nickel acetate, nickel oxide and nickel hydroxide. Sources of magnesium
include magnesium oxide, magnesium hydroxide, magnesium acetate.
Sources of manganese include manganese acetate and manganese oxide.
The new metal cation neutralized high acid ionomer resins are
produced by reacting the high acid base copolymer with various amounts of
2s the metal cation salts above the crystalline melting point of the
copolymer,
such as at a temperature from about 200°F to about 500°F,
preferably from
about 250°F to about 350°F, under high shear conditions at a
pressure of from
about 10 psi to 10,000 psi. Other well known blending techniques may also
be used. The amount of metal cation salt utilized to produce the new metal
3o cation neutralized high acid based ionomer resins is the quantity which
provides a sufficient amount of the metal cations to neutralize the desired
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percentage of the carboxylic acid groups in the high acid copolymer. The
extent of neutralization is generally from about 10% to about 90%.
As indicated below in Table 6 and more specifically in Example
1 in U.S. Application Serial No. 08/493,089, a number of new types of metal
cation neutralized high acid ionomers can be obtained from the above
indicated process. These include new high acid ionomer resins neutralized to
various extends with manganese, lithium, potassium, calcium and nickel
cations. In addition, when a high acid ethylene/acrylic acid copolymer is
utilized as the base copolymer component of the invention and this component
1o is subsequently neutralized to various extents with the metal cation salts
producing acrylic acid based high acid ionomer resins neutralized with cations
such as sodium, potassium, lithium, zinc, magnesium, manganese, calcium
and nickel, several new ration neutralized acrylic acid based high acid
ionomer
resins are produced.
Metal Cation Neutralized High Acid lonomers
Wt-% Wt-% Melt Shore
D
Formulation No. Cation NeutralizationIndex C.O.R.Hardness
Salt
1(NaOH) 6.98 67.5 0.9 0.804 71
2(NaOH) 5.66 54 2.4 0.808 73
3(NaOH) 3.84 35.9 12.2 0.812 69
4(NaOH) 2.91 27 17.5 0.812 (brittle)
5(MnAc) 19.6 71.7 7.5 0.809 73
6(MnAc) 23.1 88.3 3.5 0.814 77
7(MnAc) 15.3 53 7.5 0.81 72
8(MnAc) 26.5 106 0.7 0.813 (brittle)
9(LiOH) 4.54 71.3 0.6 0.81 74
10(LiOH) 3.38 52.5 4.2 0.818 72
11(LiOH) 2.34 35.9 18.6 0.815 72
12(KOH) 5.3 36 19.3 Broke 70
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1Nt-% 1Nt-% Melt Shore
D
Formulation Neutralization Index C.O.R.Hardness
No.
Cation
Salt
13(KOH) 8.26 57.9 7.18 0.804 70
14(KOH) 10.7 77 4.3 0.801 67
15(ZnAc)17.9 71.5 0.2 0.806 71
16(ZnAc)13.9 53 0.9 0.797 69
17(ZnAc)9.91 36.1 3.4 0.793 67
18(MgAc)17.4 70.7 2.8 0.814 74
19(MgAc)20.6 87.1 1.5 0.815 76
20(MgAc)13.8 53.8 4.1 0.814 74
21 (CaAc)13.2 69.2 1.1 0.813 74
22(CaAc)7.12 34.9 10.1 0.808 70
Controls:50/50 Blend
of loteks
800017030
C.O.R.=.810/65
Shore D Hardness
DuPont High
Acid Surlyn~
8422 (Na)
C.O.R.=.811/70
Shore D Hardness
DuPont High
Acid Surlyn~
8162 (Zn)
C.O.R.=.807/65
Shore D Hardness
Exxon High
Acid lotek
EX-960 (Zn)
C.O.R.=.796/65
Shore D Hardness
TALE 6 i(continued)
1Nt-% 1Nt-% Melt
Formulation Neutralization Index C.O.R.
No.
Cation
Salt
23(Mg0) 2.91 53.5 2.5 0.813
24(Mg0) 3.85 71.5 2.8 0.808
25(Mg0) 4.76 89.3 1.1 0.809
26(Mg0) 1.96 35.7 7.5 0.815
Control
for
Formulations
23-26
is 50/50
lotek
8000/7030,
C.O.R.=.814, Formulationwas normalized to that control
26 C.O.R. accordingly
TABLE 6 i(continuedl_
1Nt-% Wt-% Melt Shore
D
Formulation Neutralization Index C.O.R.Hardness
No.
Cation
Salt
27(NiAc)13.04 61.1 0.2 0.802 71
28(NiAc)10.71 48.9 0.5 0.799 72
29(NiAc)8.26 36.7 1.8 0.796 69
30(NiAc)5.66 24.4 7.5 0.786 64
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Control for Formulation Nos. 27-30 is 50/50 lotek 8000/7030, C.O.R.=.807
When compared to low acid versions of similar cation neutralized
ionomer resins, the new metal cation neutralized high acid ionomer resins
exhibit enhanced hardness, modulus and resilience characteristics. These are
properties that are particularly desirable in a number of thermoplastic
fields,
including the field of golf ball manufacturing.
When utilized in the construction of the inner layer of a multi-
layered golf ball, it has been found that the new acrylic acid based high acid
ionomers extend the range of hardness beyond that previously obtainable
1o while maintaining the beneficial properties (i.e. durability, click, feel,
etc.) of the
softer low acid ionomer covered balls, such as balls produced utilizing the
low
acid ionomers disclosed in U.S. Patent Nos. 4,884,814 and 4,911,451.
Moreover, as a result of the development of a number of new
acrylic acid based high acid ionomer resins neutralized to various extents by
~5 several different types of metal cations, such as manganese, lithium,
potassium, calcium and nickel cations, several new ionomers or ionomer
blends are now available for production of an inner cover layer of a multi-
layered golf ball. By using these high acid ionomer resins, harder, stiffer
inner
cover layers having higher C.O.R.s, and thus longer distance, can be obtained.
2o More preferably, it has been found that when two or more of the
above-indicated high acid ionomers, particularly blends of sodium and zinc
high acid ionomers, are processed to produce the covers of multi-layered golf
balls, (i.e., the inner cover layer herein) the resulting golf balls will
travel further
than previously known multi-layered golf balls produced with low acid ionomer
2s resin covers due to the balls' enhanced coefficient of restitution values.
The low acid ionomers which may be suitable for use in
formulating the inner layer compositions of several of the embodiments of the
subject invention are ionic copolymers which are the metal, i.e., sodium,
zinc,
magnesium, etc., salts of the reaction product of an olefin having from about
30 2 to 8 carbon atoms and an unsaturated monocarboxylic acid having from
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about 3 to 8 carbon atoms. Preferably, the ionomeric resins are copolymers
of ethylene and either acrylic or methacrylic acid. In some circumstances, an
additional comonomer such as an acrylate ester (i.e., iso- or n-butylacrylate,
etc.) can also be included to produce a softer terpolymer. The carboxylic acid
s groups of the copolymer are neutralized or partially neutralized (i.e.,
approximately 10-100%, preferably 30 - 70%) by the metal ions. Each of the
low acid ionomer resins which may be included in the inner layer cover
compositions of the invention contains 16% by weight or less of a carboxylic
acid.
The inner layer compositions include the low acid ionomers such
as those developed and sold by E.I. DuPont de Nemours 8~ Company under
the trademark "Surlyn~" and by Exxon Corporation under the trademark
"EscorT""" or tradename "lotek," or blends thereof.
The low acid ionomer resins available from Exxon under the
15 designation "EscorT""" and/or "lotek," are somewhat similar to the low acid
ionomeric resins available under the "Surlyn~" trademark. However, since the
EscorT""/lotek ionomeric resins are sodium or zinc salts of polyethylene-
acrylic
acid) and the "Surlyn~" resins are zinc, sodium, magnesium, etc. salts of
polyethylene-methacrylic acid), distinct differences in properties exist.
20 When utilized in the construction of the inner layer of a multi-
layered golf ball, it has been found that the low acid ionomer blends extend
the
range of compression and spin rates beyond that previously obtainable. IVlore
preferably, it has been found that when two or more low acid ionomers,
particularly blends of sodium and zinc ionomers, are processed to produce the
2s covers of multi-layered golf balls, (i.e., the inner cover layer herein)
the
resulting golf balls will travel further and at an enhanced spin rate than
previously known multi-layered golf balls. Such an improvement is particularly
noticeable in enlarged or oversized golf balls.
The use of an inner layer formulated from blends of lower acid
3o ionomers produces multi-layer golf balls having enhanced compression and
spin rates. These are the properties desired by the more skilled golfer.
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In yet another embodiment of the inner cover layer, a blend of
high and low acid ionomer resins is used. These can be the ionomer resins
described above, combined in a weight ratio which preferably is within the
range of 10:90 to 90:10 parts of high and low acid ionomer resins.
s A further additional embodiment of the inner cover layer is
primarily based upon the use of a fully non-ionomeric thermoplastic material.
Suitable non-ionomeric materials include metallocene catalyzed polyolefins or
polyamides, polyamide/ionomer blends, polyphenylene ether/ionomer blends,
etc., which have a shore D hardness of ?60 and a flex modulus of greater than
about 30,000 psi, or other hardness and flex modulus values which are
comparable to the properties of the ionomers described above. Other suitable
materials include but are not limited to thermoplastic or thermosetting
polyurethanes, a polyester elastomer such as that marketed by DuPont under
the trademark HytreIT""(polyether ester), or a polyether amide such as that
15 marketed by Elf Atochem S.A. under the trademark Pebax~, a blend of two or
more non-ionomeric thermoplastic elastomers, or a blend of one or more
ionomers and one or more non-ionomeric thermoplastic elastomers.
ii. Outer Cover Layer
While the dual core component described below, and the hard
2o inner cover layer formed thereon, provide the multi-layer golf ball with
power
and distance, the outer cover layer 16 is comparatively softer than the inner
cover layer. The softness provides for the feel and playability
characteristics
typically associated with balata or balata-blend balls. The outer cover layer
or
ply is comprised of a relatively soft, low modulus (about 1,000 psi to about
25 10,100 psi) and, in an alternate embodiment, low acid (less than 16 weight
percent acid) ionomer, an ionomer blend, a non-ionomeric thermoplastic or
thermosetting material such as, but not limited to, a metallocene catalyzed
polyolefin such as EXACTT"" material available from EXXON~, a polyurethane,
a polyester elastomer such as that marketed by DuPont under the trademark
3o HytreIT"", or a polyether amide such as that marketed by Elf Atochem S.A.
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under the trademark Pebax~, a blend of two or more non-ionomeric
thermoplastic or thermosetting materials, or a blend of one or more ionomers
and one or more non-ionomeric thermoplastic materials.
The outer layer is fairly thin (i.e. from about 0.010 to about 0.10
s inches in thickness, more desirably 0.03 to 0.06 inches in thickness for a
1.680
inch ball and 0.03 to 0.06 inches in thickness for a 1.72 inch or more ball),
but
thick enough to achieve desired playability characteristics while minimizing
expense. Thickness is defined as the average thickness of the non-dimpled
areas of the outer cover layer. The outer cover layer, such as layer 16, has
a Shore D hardness of at least 1 point softer than the inner cover or Shore D
of 57 or less.
In one embodiment, the outer cover layer preferably is formed
from an ionomer which constitutes at least 75 weight % of an acrylate ester-
containing ionic copolymer or blend of acrylate ester-containing ionic
~s copolymers. This type of outer cover layer in combination with the core and
inner cover layer described above results in golf ball covers having a
favorable
combination of durability and spin rate. The one or more acrylate ester-
containing ionic copolymers each contain an olefin, an acrylate ester, and an
acid. In a blend of two or more acrylate ester-containing ionic copolymers,
2o each copolymer may contain the same or a different olefin, acrylate ester
and
acid than are contained in the other copolymers. Preferably, the acrylate
ester-containing ionic copolymer or copolymers are terpolymers, but additional
monomers can be combined into the copolymers if the monomers do not
substantially reduce the scuff resistance or other good playability properties
of
25 the cover.
For a given copolymer, the olefin is selected from the group
consisting of olefins having 2 to 8 carbon atoms, including, as non-limiting
examples, ethylene, propylene, butane-1, hexane-1 and the like. Preferably
the olefin is ethylene.
3o The acrylate ester is an unsaturated monomer having from 1 to
21 carbon atoms which serves as a softening comonomer. The acrylate ester
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preferably is methyl, ethyl, n-propyl, n-butyl, n-octyl, 2-ethylhexyl, or 2-
methoxyethyl 1-acrylate, and most preferably is methyl acrylate or n-butyl
acrylate. Another suitable type of softening comonomer is an alkyl vinyl ether
selected from the group consisting of n-butyl, n-hexyl, 2-ethylhexyl, and 2-
methoxyethyl vinyl ethers.
The acid is a mono- or dicarboxylic acid and preferably is
selected from the group consisting of methacrylic, acrylic, ethacrylic, a-
chloroacrylic, crotonic, malefic, fumaric, and itaconic acid, or the like, and
half
esters of malefic, fumaric and itaconic acid, or the like. The acid group of
the
~o copolymer is 10-100% neutralized with any suitable cation, for example,
zinc,
sodium, magnesium, lithium, potassium, calcium, manganese, nickel,
chromium, tin, aluminum, or the like. It has been found that particularly good
results are obtained when the neutralization level is about 50-100%.
The one or more acrylate ester-containing ionic copolymers each
~5 has an individual Shore D hardness of about 5-64. The overall Shore D
hardness of the outer cover is 57 or less, and generally is 40-55. It is
preferred that the overall Shore D hardness of the outer cover is in the range
of 40-50 in order to impart particularly good playability characteristics to
the
ball.
2o The outer cover layer of the invention is formed over a core to
result in a golf ball having a coefficient of restitution of at least 0.760,
more
preferably at least 0.770, and most preferably at least 0.780. The coefficient
of restitution of the ball will depend upon the properties of both the core
and
the cover. The PGA compression of the golf ball is 100 or less, and preferably
25 is 90 or less.
The acrylate ester-containing ionic copolymer or copolymers used
in the outer cover layer can be obtained by neutralizing commercially
available
acrylate ester-containing acid copolymers such as polyethylene-methyl
acrylate-acrylic acid terpolymers, including ESCORT"" ATX (Exxon Chemical
3o Company) or poly (ethylene-butyl acrylate-methacrylic acid) terpolymers,
including IVIJCREL~ (DuPont Chemical Company). Particularly preferred
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commercially available materials include ATX 320, ATX 325, ATX 310, ATX
350, and blends of these materials with NUCREL~ 010 and NUCREL~ 035.
The acid groups of these materials and blends are neutralized with one or
more of various cation salts including zinc, sodium, magnesium, lithium,
potassium, calcium, manganese, nickel, etc. The degree of neutralization
ranges from 10-100%. Generally, a higher degree of neutralization results in
a harder and tougher cover material. The properties of non-limiting examples
of commercially available un-neutralized acid terpolymers which can be used
to form the golf ball outer cover layers of the invention are provided below
in
1o Table 7.
TABLE 7
Properties of Un-Neutralized Acid Terpolyrmers
Flex
Melt Index Modulus
dg/min Acid No. MPa Hardness
Trade Name ASTM D 1238 % KOH/p (ASTM D790) Shore
D
ATX 310 6 45 80 44
ATX 320 5 45 50 34
ATX 325 20 45 9 30
ATX 350 6 15 20 28
Nucrel~ 010 11 60 40 40
Nucrel~ 035 35 60 59 40
2o The ionomer resins used to form the outer cover layers can be
produced by reacting the acrylate ester-containing acid copolymer with various
amounts of the metal cation salts at a temperature above the crystalline
melting point of the copolymer, such as a temperature from about 200°F
to
about 500°F, preferably from about 250°F to about 350°F,
under high shear
2s conditions at a pressure of from about 100 psi to 10,000 psi. Other well
known blending techniques may also be used. The amount of metal cation
salt utilized to produce the neutralized ionic copolymers is the quantity
which
provides a sufficient amount of the metal rations to neutralize the desired
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percentage of the carboxylic acid groups in the high acid copolymer. When
two or more different copolymers are to be used, the copolymers can be
blended before or after neutralization. Generally, it is preferable to blend
the
copolymers before they are neutralized to provide for optimal mixing.
The compatibility of the acrylate ester-containing copolymers with
each other in a copolymer blend produces a golf ball outer cover layer having
a surprisingly good scuff resistance for a given hardness of the outer cover
layer. The golf ball according to the invention has a scuff resistance of no
higher than 3Ø It is preferred that the golf ball has a scuff resistance of
no
~o higher than about 2.5 to ensure that the golf ball is scuff resistant when
used
in conjunction with a variety of types of clubs, including sharp-grooved
irons,
which are particularly inclined to result in scuffing of golf ball covers. The
best
results according to the invention are obtained when the outer cover layer has
a scuff resistance of no more than about 2Ø
~5 Additional materials may also be added to the inner and outer
cover layer of the present invention as long as they do not substantially
reduce
the playability properties of the ball. Such materials include dyes (for
example,
Ultramarine BIueT"" sold by Whitaker, Clark, and Daniels of South Plainsfield,
N.J.) (see U.S. Pat. No. 4,679,795), pigments such as titanium dioxide, zinc
20 oxide, barium sulfate and zinc sulfate; UV absorbers; optical brighteners
such
as EastobriteT"" OB-1 and UvitexT"" OB antioxidants; antistatic agents; and
stabilizers. Moreover, the cover compositions of the present invention may
also contain softening agents such as those disclosed in U.S. Patent Nos.
5,312,857 and 5,306,760, including plasticizers, metal stearates, processing
2s acids, etc., and reinforcing materials such as glass fibers and inorganic
fillers,
as long as the desired properties produced by the golf ball covers of the
invention are not impaired.
The outer layer in another embodiment of the invention includes
a blend of a soft (low acid) ionomer resin with a small amount of a hard (high
3o acid) ionomer resin. A low modules ionomer suitable for use in the outer
layer
blend has a flexural modules measuring from about 1,000 to about 10,000 psi,
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with a hardness of about 20 to about 40 on the Shore D scale. A high
modulus ionomer herein is one which measures from about 15,000 to about
70,000 psi as measured in accordance with ASTM method D-790. The
hardness may be defined as at least 50 on the Shore D scale as measured in
accordance with ASTM method D-2240, but on the ball and not on a plaque.
Soft ionomers primarily are used in formulating the hard/soft
blends of the cover compositions. These ionomers include acrylic acid and
methacrylic acid based soft ionomers. They are generally characterized as
comprising sodium, zinc, or other mono- or divalent metal cation salts of a
terpolymer of an olefin having from about 2 to 8 carbon atoms, methacrylic
acid, acrylic acid, or another, a, (3- unsaturated carboxylic acid, and an
unsaturated monomer of the acrylate ester class having from 1 to 21 carbon
atoms. The soft ionomer is preferably made from an acrylic acid base polymer
is an unsaturated monomer of the acrylate ester class.
~5 Certain ethylene-acrylic acid based soft ionomer resins developed
by the Exxon Corporation under the designation "lotek 7520" (referred to
experimentally by differences in neutralization and melt indexes as LDX 195,
LDX 196, LDX 218 and LDX 219) may be combined with known hard ionomers
such as those indicated above to produce the inner and outer cover layers.
2o The combination produces higher C.O.R.s at equal or softer hardness, higher
melt flow, (which corresponds to improved, more efficient molding, i.e., fewer
rejects) as well as significant cost savings versus the outer layer of multi-
layer
balls produced by other known hard-soft ionomer blends as a result of the
lower overall raw materials cost and improved yields.
25 While the exact chemical composition of the resins to be sold by
Exxon under the designation lotek 7520 is considered by Exxon to be
confidential and proprietary information, Exxon's experimental product data
sheet lists the following physical properties of the ethylene acrylic acid
zinc
ionomer developed by Exxon:
30 TALE 8
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Ph ysical Properties
of lotek 7520
Property Value ASTM Method Units Tvaical
Melt Index D-1238 g/10 min. 2
Density D-1505 kg/m3 0.962
Cation Zinc
Melting Point D-3417 C 66
Crystallization
Point D-3417 C 49
Vicat Softening
1o Point D-1525 C 42
Plaque Properties (2
mm thick Compression
Molded Plaques
Tensile at Break D-638 MPa 10
Yield Point D-638 MPa None
Elongation at Break D-638 % 760
~5 1 % Secant Modulus D-638 MPa 22
Shore D Hardness D-2240 32
Flexural Modulus D-790 MPa 26
Zwick Rebound ISO 4862 % 52
De Mattia Flex
2o Resistance D-430 Cycles >5000
In addition, test data collected by the inventor indicates that lotek
7520 resins have Shore D hardnesses of about 32 to 36 (per ASTM D-2240),
melt flow indexes of 310.5 g/10 min (at 190°C. per ASTM D-1288), and a
flexural modulus of about 2500 - 3500 psi (per ASTM D-790). Furthermore,
2~ testing by an independent testing laboratory by pyrolysis mass spectrometry
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indicates at lotek 7520 resins are generally zinc salts of a terpolymer of
ethylene, acrylic acid, and methyl acrylate.
Furthermore, the inventor has found that a newly developed
grade of an acrylic acid based soft ionomer available from the Exxon
Corporation under the designation lotek 7510 is also effective when combined
with the hard ionomers indicated above in producing golf ball covers
exhibiting
higher C.O.R. values at equal or softer hardness than those produced by
known hard-soft ionomer blends. In this regard, lotek 7510 has the
advantages (i.e. improved flow, higher C.O.R. values at equal hardness,
1o increased clarity, etc.) produced by the lotek 7520 resin when compared to
the
methacrylic acid base soft ionomers known in the art (such as the Surlyn~
8625 and Surlyn~ 8629 combinations disclosed in U.S. Patent No. 4,884,814).
In addition, lotek 7510, when compared to lotek 7520, produces
slightly higher C.O.R. values at equal softness/hardness due to the lotek
7510's higher hardness and neutralization. Similarly, lotek 7510 produces
better release properties (from the mold cavities) due to its slightly higher
stiffness and lower flow rate than lotek 7520. This is important in production
where the soft covered balls tend to have lower yields caused by sticking in
the molds and subsequent punched pin marks from the knockouts.
2o According to Exxon, lotek 7510 is of similar chemical composition
as lotek 7520 (i.e. a zinc salt of a terpolymer of ethylene, acrylic acid, and
methyl acrylate) but is more highly neutralized. Based upon FTIR analysis,
lotek 7520 is estimated to be about 30-40 wt.-% neutralized and lotek 7510 is
estimated to be about 40-60 wt.-% neutralized. The typical properties of lotek
2s 7510 in comparison of those of lotek 7520 in comparison of those of lotek
7520 are set forth below:
TALE 9
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Physical Pro~~erties of lotek 7510
in Comparison to lotek 7520
IOTEK 7520 IOTEK 7510
MI, g/10 min 2.0 0.8
Density, g/cc 0.96 0.97
Melting Point, F 151 149
Vicat Softening Point, F 108 109
Flex Modulus, psi 3800 5300
Tensile Strength, psi 1450 1750
Elongation, % 760 690
Hardness, Shore D 32 35
The hard ionomer resins utilized to produce the outer cover layer
composition hard/soft blends include ionic copolymers which are the sodium,
~5 zinc, magnesium, lithium, etc. salts of the reaction product of an olefin
having
from 2 to 8 carbon atoms and an unsaturated monocarboxylic acid having from
3 to 8 carbon atoms. The carboxylic acid groups of the copolymer may be
totally or partially (i.e. approximately 15-75 percent) neutralized.
The hard ionomeric resins are likely copolymers of ethylene and
2o acrylic and/or methacrylic acid, with copolymers of ethylene and acrylic
acid
being the most preferred. Two or more types of hard ionomeric resins may be
blended into the outer cover layer compositions in order to produce the
desired
properties of the resulting golf balls.
As discussed earlier herein, the hard ionomeric resins introduced
25 under the designation EscorTM and sold under the designation "lotek" are
somewhat similar to the hard ionomeric resins sold under the Surlyn~
trademark. However, since the "lotek" ionomeric resins are sodium or zinc
salts of polyethylene-acrylic acid) and the Surlyn~ resins are zinc or sodium
salts of polyethylene-methacrylic acid) some distinct differences in
properties
3o exist. As more specifically indicated in the data set forth below, the hard
"lotek" resins (i.e., the acrylic acid based hard ionomer resins) are the more
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preferred hard resins for use in formulating the outer layer blends for use in
the present invention. In addition, various blends of "lotek" and Surlyn~ hard
ionomeric resins, as well as other available ionomeric resins, may be utilized
in the present invention in a similar manner.
s Examples of commercially available hard ionomeric resins which
may be used in the present invention in formulating the outer cover blends
include the hard sodium ionic copolymer sold under the trademark Surlyn~
8940 and the hard zinc ionic copolymer sold under the trademark Surlyn~
9910. Surlyn~ 8940 is a copolymer of ethylene with methacrylic acid and
about 15 weight percent acid which is about 29 percent neutralized with
sodium ions. This resin has an average melt flow index of about 2.8. Surlyn~
9910 is a copolymer of ethylene and methacrylic acid with about 15 weight
percent acid which is about 58 percent neutralized with zinc ions. The
average melt flow index of Surlyn~ 9910 is about 0.7. The typical properties
15 of Surlyn~ 9910 and 8940 are set forth below in Table 10:
TABLE 10
Typical Properties of Commercially Available Hard
Sur~rn~ Resins Suitable for Use in the Outer Layrer Blends
of the Present Invention
20 ASTM D 8940 99108920 8528 99709730
Cation Type Sodium ZincSodiumSodiumZincZinc
Melt flow index,
gms/10 min. D-1238 2.8 0.7 0.9 1.3 14.01.6
Specific Gravity,
25 g/cm' D-792 0.95 0.970.95 0.94 0.950.95
Hardness, Shore D-2240 66 64 66 60 62 63
D
Tensile Strength,
(kpsi), MPa D-638 (4.8) (3.6)(5.4) (4.2)(3.2)(4.1)
33.1 24.837.2 29.0 22.028.0
30 Elongation, D-638 470 290 350 450 460 460
%
Flexural Modulus,
(kpsi) MPa D-790 (51) (48)(55) (32) (28)(30)
350 330 380 220 190 210
Tensile Impact (23°C)
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KJ/m2 (ft.-Ibs./inz) D-1822S 1020 1020 865 1160 760 1240
(485) (485) (410) (550) (360) (590)
Vicat Temperature,°C D-1525 63 62 58 73 61 73
Examples of the more pertinent acrylic acid based hard ionomer
resin suitable for use in the present outer cover composition sold under the
"lotek" trade name by the Exxon Corporation include lotek 8000, 8010, 8020,
8030, 7030, 7010, 7020, 1002, 1003, 959 and 960. The physical properties
of lotek 959 and 960 are shown above. The typical properties of the
remainder of these and other lotek hard ionomers suited for use in formulating
1o the outer layer cover composition are set forth below in Table 11:
TABLE 11
Typical Properties of lotek lonomers
Resin ASTM
Properties Method Units 4000 4010 8000 8020 8030
Cation type zinc zinc sodiumsodiumsodium
Melt index D-1238 g/10 2.5 1.5 0.8 1.6 2.8
min.
Density D-1505 kg/m' 963 963 954 960 960
Melting Point D-3417 C 90 90 90 87.5 87.5
CrystallizationD-3417 C 62 64 56 53 55
Point
Vicat SofteningD-1525 C 62 63 61 64 67
Point
Weight Acrylic 16 15
Acid
of Acid Groups
ration neutralized 30 40
Plaque ASTM
Properties Method Units 4000 4010 8000 8020 8030
(3 mm thick,
compression
molded)
Tensile at breakD-638 MPa 24 26 36 31.5 28
Yield point D-638 MPa none none 21 21 23
Elongation at D-638 % 395 420 350 410 395
break
1% Secant modulusD-638 MPa 160 160 300 350 390
Shore Hardness D-2240 -- 55 55 61 58 59
D
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Film Properties
(50 micron
film 2.2:1
Blow-up ratio) 4000 4010 8000 8020 8030
Tensile at D-882MPa 41 39 42 52 47.4
Break MD
TD D-882MPa 37 38 38 38 40.5
Yield point MD D-882MPa 15 17 17 23 21.6
TD D-882MPa 14 15 15 21 20.7
Elongation
at Break
MD D-882% 310 270 260 295 305
TD D-882% 360 340 280 340 345
1% Secant MD D-882MPa 210 215 390 380 380
modulus
TD D-882MPa 200 225 380 350 345
Dart Drop D-1709g/micron 12.5 20.3
Impact 12.4
Resin ASTM
Properties MethodUnits 7010 7020 7030
Cation type zinc zinc zinc
Melt Index D-1238g/10 minØ8 1.5 2.5
Density D-1505kglm' 960 960 960
Melting Point D-3417~C 90 90 90
Crystallization
Point D-3417~C - - -
Vicat Softening
Point D-1525~C 60 63 62.5
%Weight Acrylic - - -
Acid
of Acid Groups
Cation Neutralized - - -
Plaque ASTM
Properties MethodUnits 7010 7020 7030
(3 mm thick,
compression
molded)
Tensile at D-638MPa 38 38 38
break
Yield Point D-638MPa none none none
Elongation D-638% 500 420 395
at break
1% Secant D-638MPa -- -- -
modulus
Shore Hardness D-2240- 57 55 55
D
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It has been determined that when hard/soft ionomer blends are
used for the outer cover layer, good results are achieved when the relative
combination is in a range of about 3-25 percent hard ionomer and about 75-97
percent soft ionomer.
Moreover, in alternative embodiments, the outer cover layer
formulation may also comprise up to 100 wt % of a soft, low modulus non-
ionomeric thermoplastic material including a polyester polyurethane such as
B.F. Goodrich Company's Estane~ polyester polyurethane X-4517. The non-
ionomeric thermoplastic material may be blended with a soft ionomer. For
example, polyamides blend well with soft ionomer. According to B.F.
Goodrich, Estane~ X-4517 has the following properties:
Properties of Estane~ X-4517
Tensile 1430
100% 815
200% 1024
300% 1193
Elongation 641
Youngs Modulus 1826
Hardness A/D 88/39
2o Bayshore Rebound 59
Solubility in Water Insoluble
Melt processing temperature >350~F (>177~C)
Specific Gravity (H20=1) 1.1-1.3
Other soft, relatively low modulus non-ionomeric thermoplastic
elastomers may also be utilized to produce the outer cover layer as long as
the non-ionomeric thermoplastic elastomers produce the playability and
durability characteristics desired without adversely effecting the enhanced
travel distance characteristic produced by the high acid ionomer resin
composition. These include, but are not limited to, thermoplastic
3o polyurethanes such as TexinT"", thermoplastic polyurethanes from Mobay
Chemical Co. and the PellethaneT"" thermoplastic polyurethanes from Dow
Chemical Co.; non-ionomeric thermoset polyurethanes including but not limited
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to those disclosed in U.S. Patent 5,334,673; cross-linked metallocene
catalyzed polyolefins; ionomer/rubber blends such as those in Applicants' U.S.
Patents 4,986,545; 5,098,105 and 5,187,013; and, HytreIT"" polyester
elastomers from DuPont and Pebax~ polyetheramides from Elf Atochem S.A.
s B. Single Layer Covers
The cores of the present invention can also be covered by a
single cover layer. Preferably, the single layer covers are comprised of the
outer layer cover materials discussed above. Additionally, the single layer
covers can also comprise the inner cover materials referenced above.
Method of Making Golf Ball
In preparing golf balls in accordance with the present invention,
a cover layer is molded (by injection molding or by compression molding)
about a core (a dual core).
The dual cores of the present invention are preferably formed by
~5 the compression molding techniques set forth above. However, it is fully
contemplated that liquid injection molding or transfer molding techniques
could
also be utilized.
A relatively hard inner cover layer is then molded about the
resulting dual core component. The diameter of the inner cover is about 1.570
2o inches. A comparatively softer outer cover layer is then molded about the
inner cover layer. The outer cover diameter is about 1.680 inches. Details of
molding the inner and outer covers are set forth herein. Alternatively, a
single
soft cover can be molded around the dual core.
Generally, the inner cover layer which is molded over the dual
25 core component, is about 0.01 inches to about 0.10 inches in thickness,
preferably about 0.03-0.07 inches thick. The inner ball which includes the
core
and inner cover layer preferably has a diameter in the range of 1.25 to 1.60
inches. The outer cover layer is about 0.01 inches to about 0.10 inches in
thickness. Together, the dual core, the inner cover layer and the outer cover
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layer combine to form a ball having a diameter of 1.680 inches or more, the
minimum diameter permitted by the rules of the United States Golf Association
and weighing no more than 1.62 ounces.
Most preferably, the resulting golf balls in accordance with the
s present invention have the following dimensions:
Size Specifications: Range Preferred
Inner Core - Max. 0.830" 0.344"
- Min. 0.200" 0.340"
Outer Core - Max. 1.60" 1.595"
- Min. 1.25" 1.47"
Cover Thickness
- Max. 0.215" 0.065"
- Min. 0.040" 0.040"
In a particularly preferred embodiment of the invention, the golf
15 ball has a dimple pattern which provides coverage of 60% -70% or more. The
golf ball typically is coated with a durable, abrasion-resistant, relatively
non-
yellowing finish coat.
The various cover composition layers of the present invention
may be produced according to conventional melt blending procedures.
2o Generally, the copolymer resins are blended in a BanburyT"" type mixer, two-
roll mill, or extruder prior to neutralization. After blending, neutralization
then
occurs in the melt or molten states in the BanburyT"" mixer. Mixing problems
are minimal because preferably more than 75 wt %, and more preferably at
least 80 wt % of the ionic copolymers in the mixture contain acrylate esters
2s and, in this respect, most of the polymer chains in the mixture are similar
to
each other. The blended composition is then formed into slabs, pellets, etc.,
and maintained in such a state until molding is desired.
Alternatively, a simple dry blend of the pelletized or granulated
resins which have previously been neutralized to a desired extent and colored
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masterbatch may be prepared and fed directly into the injection molding
machine where homogenization occurs in the mixing section of the barrel prior
to injection into the mold. If necessary, further additives such as an
inorganic
filler, etc., may be added and uniformly mixed before initiation of the
molding
process. A similar process is utilized to formulate the high acid ionomer
resin
compositions used to produce the inner cover layer. In one embodiment of the
invention, a masterbatch of non-acrylate ester-containing ionomer with
pigments and other additives incorporated therein is mixed with the acrylate
ester-containing copolymers in a ratio of about 1 - 7 weight % masterbatch and
93 - 99 weight % acrylate ester-containing copolymer. However, a
masterbatch is generally not used commercially to form the inner cover or
mantle layer due to cost concerns.
The golf balls of the present invention can also be produced by
molding processes which include but are not limited to those which are
~5 currently well known in the golf ball art. For example, the golf balls can
be
produced by injection molding or compression molding the novel cover
compositions around a solid molded core to produce an inner ball which
typically has a diameter of about 1.25 to 1.60 inches. The core, preferably of
a dual core configuration, may be formed as previously described. The outer
layer is subsequently molded over the inner layer to produce a golf ball
having
a diameter of preferably about 1.680 inches or more.
In compression molding, the inner cover composition is formed
via injection at about 380°F to about 450°F into smooth surfaced
hemispherical
shells which are then positioned around the core in a mold having the desired
inner cover thickness and subjected to compression molding at 200° to
300°F
for about 2 to 10 minutes, followed by cooling at 50° to 70°F
for about 2 to 7
minutes to fuse the shells together to form a unitary intermediate ball. In
addition, the intermediate balls may be produced by injection molding wherein
the inner cover layer is injected directly around the core placed at the
center
of an intermediate ball mold for a period of time in a mold temperature of
from
50° to about 100°F. Subsequently, the outer cover layer is
molded around the
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core and the inner layer by similar compression or injection molding
techniques
to form a dimpled golf ball of a diameter of 1.680 inches or more.
After formation of the balls, the balls are optionally subjected to
gamma radiation. This has been found to crosslink the cover to improve scuff
s and cut resistance. Furthermore, the gamma radiation has also been found
to increase the crosslink density of the core and results in a harder and
higher
compression core and ball. And so, the Shore C hardness of the core typically
increases after gamma treatment.
After molding and/or radiation treatment, the golf balls produced
may undergo various further processing steps such as buffing, painting and
marking as disclosed in U.S. Patent No. 4,911,451.
The resulting golf ball produced from the hard inner layer and the
relatively softer, low flexural modulus outer layer provide for an improved
multi-
layer golf ball having a unique dual core configuration which provides for
15 desirable coefficient of restitution and durability properties while at the
same
time offering the feel and spin characteristics associated with soft balata
and
balata-like covers of the prior art.
Golf balls according to the invention preferably have a PGA
compression of 10 -120. In a particularly preferred form of the invention, the
golf
2o balls have a PGA compression of about 40 - 100. It has been found that
excellent results are obtained when the PGA compression of the golf balls is
60 -
100. The coefficient of restitution of the golf balls of the invention is in
the range
of 0.770 or greater. Preferably, the C.O.R. of the golf balls is in the range
of .770
.830 and most preferably .790 - .830.
25 As mentioned above, resiliency and compression are amongst the
principal properties involved in a golf ball's performance. In the past, PGA
compression related to a scale of 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 -110, preferably
3o around 80 to 100.
In determining PGA compression using the 0 - 200 scale, a
standard force is applied to the external surface of the ball. A ball which
exhibits
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no deflection (0.0 inches in deflection) is rated 200 and a ball which
deflects
2/10th of an inch (0.2 inches) is rated 0. Every change of .001 of an inch in
deflection represents a 1 point drop in compression. Consequently, a ball
which
deflects 0.1 inches (100 x .001 inches) has a PGA compression value of 100
s (i.e., 200 - 100) and a ball which deflects 0.110 inches (110 x .001 inches)
has
a PGA compression of 90 (i.e., 200 -110).
In order to assist in the determination of compression, several
devices have been employed by the industry. For example, PGA compression
in determined by an apparatus fashioned in the form of a small press with an
upper and lower anvil. The upper anvil is at rest against a die spring, and
the
lower anvil is movable through 0.300 inches by means of a crank mechanism.
In its open position the gap between the anvils is 1.780 inches allowing a
clearance of 0.100 inches for insertion of the ball. As the lower anvil is
raised by
the crank, it compresses the ball against the upper anvil, such compression
~5 occurring during the last 0.200 inches of stroke of the lower anvil, the
ball then
loading the upper anvil which in turn loads the spring. The equilibrium point
of
the upper anvil is measured by a dial micrometer if the anvil is deflected by
the
ball more than 0.100 inches (less deflection is simply regarded as zero
compression) and the reading on the micrometer dial is referred to as the
2o compression of the ball. In practice, tournament quality balls have
compression
ratings around 80 to 100 which means that the upper anvil was deflected a
total
of 0.120 to 0.100 inches.
An example to determine PGA compression can be shown by
utilizing a golf ball compression tester produced by Atti Engineering
Corporation
25 of Newark, N.J., now manufactured by OK Automation of Sinking Spring, PA.
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
3o subjected to compressive loading. The Atti 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 spring loaded
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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.
Alternative devices have also been employed to determine
compression. For example, Applicants also utilize a modified Riehle
Compression Machine originally produced by Riehle Bros. Testing Machine
Company, Phil., 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 force applied by the Atti or PGA compression
tester. Using such a device, a Riehle compression of 61 corresponds to a
deflection under load of 0.061 inches.
Additionally, an approximate relationship between Riehle
compression and PGA compression exists for balls of the same size. It has been
determined by Applicants that Riehle compression corresponds to PGA
compression by the general formula PGA compression = 160 - Riehle
compression. Consequently, 80 Riehle compression corresponds to 80 PGA
2o compression, 70 Riehle corresponds to 90 PGA compression, and 60 PGA
compression corresponds to 100 PGA compression. For reporting purposes,
Applicants' compression values are usually measured as Riehle compression
and converted to PGA compression.
Furthermore, additional compression devices may also be utilized
2s to monitor golf ball compression so long as the correlation to PGA
compression
is known. These devices have been designed, such as a Whitney Tester, to
correlate or correspond to PGA compression through a set relationship or
formula.
As used herein, '°Shore D hardness" or "Shore C hardness" of a
3o core or cover component is measured generally in accordance with ASTM D-
2240, except the measurements are made on the curved surface of the molded
component, rather than on a plaque. Furthermore, the Shore C-D hardness of
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the cover is measured while the cover remains over the core. When a hardness
measurement is made on a dimpled cover, Shore C-D hardness is measured at
a land area of the dimpled cover.
Golf balls according to the invention have a cut resistance in the
s range of 1 - 3 on a scale of 1 - 5. It is preferred that the golf balls of
the invention
have a cut resistance of 1 - 2.5 and most preferably 1 - 2.
The scuff resistance test was conducted in the following manner:
a Top-Flite~ Tour pitching wedge (1994) with box grooves was obtained and was
mounted in a MiyamaeT"" driving machine. The club face was oriented for a
square hit. The forward/backward tee position was adjusted so that the tee was
four inches behind the point in the downswing where the club was vertical. The
height of the tee and the toe-heel position of the club relative to the tee
were
adjusted in order that the center of the impact mark was about 3/4 of an inch
above the sole and was centered toe to heel across the face. The machine was
~5 operated at a clubhead speed of 125 feet per second. Three samples of each
ball were tested. Each ball was hit three times. After testing, the balls were
rated according to the following table:
Rating Type of damage
1 Little or no damage (groove markings or
2o dents)
2 Small cuts and/or ripples in cover
3 Moderate amount of material lifted from ball
surface but still attached to ball
4 Material removed or barely attached
25 Cut resistance was measured in accordance with the following
procedure: A golf ball was fired at 135 feet per second against the leading
edge
of a 1994 Top-Flite~ Tour pitching wedge, wherein the leading edge radius is
1/32 inch, the loft angle is 51 degrees, the sole radius is 2.5 inches, and
the
bounce angle is 7 degrees. The cut resistance of the balls tested herein was
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evaluated on a scale of 1 - 5. A 5 represents a cut that extends completely
through the cover to the Core; a 4 represents a cut that does not extend
completely through the cover but that does break the surface; a 3 does not
break the surface of the cover but does leave a permanent dent; a 2 leaves
only
a slight crease which is permanent but not as severe as 3; and a 1 represents
virtually no visible indentation or damage of any sort.
The spin rate of the ball of the invention may be tested in the
manner described in Example 2 below.
Having generally described the invention, the following examples
are included for purposes of illustration so that the invention may be more
readily understood and are in no way intended to limit the scope of the
invention unless otherwise specifically indicated.
EXAMPLES
Example 1 Dual Core Golf Ball With Heavy Elastomeric Nucleus
Comprising a Tungsten Powderl Polybutadiene Rubber Core,
11/32" Diameter
1A. A Dual Core and a Dual Cover Golf Ball
A heavy spherical center core layer containing powdered tungsten
metal in a polybutadiene matrix and having a diameter of 0.344 inches (8.74
mm)
2o was formed with the following composition:
Components phr
Neo Cis 40 Butadiene Rubber 100.0
KuliteT"" Tungsten Powder 1248.5
(5 microns)
Iron Powder 100.0
Zinc Oxide 5.0
VaroxT~" 231XL Peroxide Initiator3.0
Zinc Diacrylate 0.0
TOTAL 1456.5
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The spherical center core layer comprising the above composition
exhibited a specific gravity of 7.65, a weight of 2.7 grams, and a Shore C
hardness of 80 (preferred range is 50-95).
The iron powder of the above composition was optional and was
added to the composition in order to attract the formed center to a magnet.
Such attraction allows for automated assembly of the 0.344 inch spherical
center to the uncured preformed half shells in golf ball production.
As mentioned above, zinc diacrylate (ZDA) is not included in the
composition of the center core layer of the present invention. Zinc diacrylate
1o is normally added to core compositions in golf ball production in order to
increase hardness.
An outer core layer was disposed about the spherical center core
layer presented above. The outer core layer had the following composition:
Components phr
BCP-820 40
Neo Cis 40 30
Neo Cis 60 30
Zinc Oxide 13.7
Zinc Stearate 16
Zinc Diacrylate 21.3
Trigonox 42-40 1.25
Total 152.25
The molded dual core comprising a spherical center and outer
core layer with the above compositions exhibited the following properties:
Molded Dual Core Properties
Size (inches) 1.478 (37.5 mm)
Weight (grams) 32.83
Riehle Compression 140 (.140 inches of deformation)
C.O. R. 0.768
Specific Gravity 1.10
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A centerless ground dual core comprising a spherical center and
outer core layer with the above compositions exhibited the following
properties:
Centerless Ground Dual Core
Properties
Size (inches) 1.469 (37.3 mm)
Weight (grams) . 32.24
Riehle Compression 137 (.137 inches)
C.O.R. 0.774
Specific Gravity 1.18
In torming a mufti-layered golt ball composing the dual core
1o having a spherical center core layer and an outer core layer with the above
compositions, the following inner cover layer, i.e., mantle layer, composition
was used:
Inner Cover (Mantle) Layer
Composition
Components phr
lotek 1002 50
lotek 1003 50
Total 100
Upon the formation of the inner cover layer on the dual core to
form an intermediate ball, the combination of an inner cover layer and dual
2o core exhibited the following properties:
Combination of Inner Cover
Layer and Dual Core Properties
Size (inches) 1.570
Weight (grams) 38.3
Riehle Compression 113 (.113 inches)
C.O.R. 0.803
Shore D 68-72
Specific Gravity 1.15
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An outer cover layer was disposed about the inner cover layer
having the following formulation:
Outer Cover Layer Composition
Components Parts by Weight
lotek 7510 41
lotek 7520 49.5
White M.B.' 9.5
~wnrte nn.t~. compnses the ronov~nng composmon:
100 pts. Surlyn AD8549
31.3 pts. Unitane 0-110
0.60 pts. Ultra Marine Blue
0.34 pts. Eastobrite O&1
0.05 pts. Santonox R
The molded balls may optionally be subjected to gamma radiation
~5 treatment at about 40 kilograys to crosslink the cover to improve scuff and
cut
resistance. The gamma radiation also increases the crosslink density of the
core and results in a harder core and ball compression. Below is a
comparison of properties exhibited by a golf ball prior to gamma radiation and
properties exhibited by a golf ball subjected to gamma radiation:
20 Dual Core,
Multi-Layered,
Golf Ball
Properties
Golf Ball Size (inches)Weight (grams)Riehle C.O.R..
Compression
Molded Ball1.685 45.2 104 0.789
Before Gamma (.104 inches)
Radiation
25 Molded Ball1.683 45.2 87 0.805
After Gamma
(.087 inches)
Radiation
Finished 1.684 45.3 87 0.805
Golf
Ball (.087 inches)
30 1 Be A Dual Core and Single Layer Golf Ball
A spherical center core layer having a diameter of 0.344 inches
was formed with the following composition:
Components phr
Neo Cis 40 Butadiene Rubber 100.0
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Kulite Tungsten Powder (5 1248.5
microns)
Iron Powder 100.0
Zinc Oxide 5.0
Varox 231XL Peroxide 3.0
Zinc Diacrylate 0.0
TOTAL 1456.5
The spherical center comprising the above composition exhibited
a specific gravity of 7.65, a weight of 2.7 grams, and a Shore C hardness of
80.
Again, the iron powder of the above composition was again optional
and was added to the composition in order to attract the composition to a
magnet. As mentioned above, such attraction allows for automated assembly
of the 0.344 inch spherical center to the uncured preformed half shells in
golf ball
production.
An outer core layer was disposed about the spherical center having
~s the following composition:
Components phr
BC P-820 40
Neo Cis 40 30
Neo Cis 60 30
20 Zinc Oxide 9.5
Zinc Stearate 16
Zinc Diacrylate 29
Trignonox 42-40 1.25
Total 155.75
2s The molded dual core comprising a spherical center core layer and
an outer core layer with the above compositions exhibited the following
properties:
Molded Dual Core Properties
(with °i1/32" Heavy Weight Spherical Center)
30 Size (inches) 1.559
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Weight (grams) 38.1
Riehle Compression 94 (0.094")
C.O.R. 0.799
Specific Gravity 1.11
A single layer cover was disposed about the dual core having the
following composition:
Cover Layer Composition
Components Parts by Weight
lotek 7510 41
lotek 7520 49.5
White M.B.' 9.5
Total 100
~wnne nn.rs. compnses the tonov~nng composroon:
100 pts. Suriyn AD8549
31.3 pts. Unitane 0-110
0.60 pts. URra Marine Blue
0.34 pts. Eastobrite OB-1
0.05 pts. Santonox R
Once again, the molded balls may optionally be subjected to
2o gamma radiation treatment at about 40 kilograys to crosslink the cover to
improve scuff and cut resistance. The gamma radiation also increases the
crosslink density of the core and results in a harder core and ball
compression.
Below is a comparison of properties exhibited by a golf ball prior to gamma
radiation and properties exhibited by a golf ball subjected to gamma
radiation:
Dual Core,
Single-Layered
Golf Ball
Properties
Golf Ball Size (inches)Weight (grams)Riehle C.O.R.
Compression
Molded Ball1.684 45.8 96 0.792
Before Gamma (.096 inches)
Radiation
Molded Ball1.681 45.8 77 0.814
After Gamma (.077 inches)
Radiation
Finished 1.682 45.9 76 0.816
Golf
Ball (.076 inches)
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Example 2
Spin rate testing was conducted with the finished multi-layered
covered, dual core golf balls (Example 1A) and single-layered cover, dual core
golf balls (Example 1 B) of above Example using a driver, a 5 iron, a 9 iron,
s and a pitching wedge. The golf ball testing machine was set up to emulate
the
launch conditions of an average Touring Professional Golfer for each
particular
club. For comparative purposes, commercial golf balls were also tested for
spin rate using the same clubs.
Below are the results of the spin rate testing:
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d
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_87_
The above results indicate that the solid, non-wound golf balls
having a heavy elastomeric center exhibit enhanced overall high spin
properties.
Example 3
s One half of the polybutadiene rubber utilized in the inner core of
Examples 1-2 was deleted and substituted with polyisoprene. Specifically, 50
phr of Natsyn 2000 was substituted for Neo-Cis 40 according to the following
formula:
ACTUAL
MATERIAL PHR Sp. Gr.
Enichem Neo Cis 40 50.00 0.910
Goodyear Natsyn 2200 50.00 0.910
Kulite Tungsten Powder1386.40 19.350
(5 microns)
Aldrich Iron Oxide, 64.90 5.100
Fe3o4
(less than 5 microns)
Zinc Oxide 5.00 5.570
Varox 231 XL 7.50 1.410
TOTALS 1563.80 7.800
Inner cores having the following properties were produced:
J~ecifications:
size: 0.340 inches, ~ 0.006 inches
weight: 2.77 grams, t 0.1 grams
hardness: 62 Shore C peak t 5 points
The inner cores, when enclosed with the above outer core and
2s cover formulations, produced golf balls exhibiting the enhanced
characteristics
of the balls of Example 1.
The invention has been described with reference to the preferred
embodiments. Obviously, modifications and alterations will occur to others
upon a reading and understanding the preceding detailed description. It is
3o intended that the invention be construed as including all such
modifications
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_gg_
and alterations in so far as they come within the scope of the appended claims
or the equivalents thereof.
