U.S. patent application number 09/842829 was filed with the patent office on 2002-10-31 for all rubber golf ball with hoop-stress layer.
Invention is credited to Halko, Roman D., Morgan, William E., Vieira, Emanuel.
Application Number | 20020160859 09/842829 |
Document ID | / |
Family ID | 25288338 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020160859 |
Kind Code |
A1 |
Morgan, William E. ; et
al. |
October 31, 2002 |
All rubber golf ball with hoop-stress layer
Abstract
The invention includes a golf ball having a core, a hoop-stress
layer of high tensile elastic modulus material wrapped or wound
about the core, at least one outermost layer of a thermoset
material having a thickness of greater than about 0.065 inches. A
binding material can be used in conjunction with the hoop-stress
layer to facilitate positioning of the hoop-stress layer around the
core for easier manufacturing.
Inventors: |
Morgan, William E.;
(Barrington, RI) ; Halko, Roman D.; (San Diego,
CA) ; Vieira, Emanuel; (New Bedford, MA) |
Correspondence
Address: |
SWIDLER BERLIN SHEREFF FRIEDMAN, LLP
3000 K STREET, NW
BOX IP
WASHINGTON
DC
20007
US
|
Family ID: |
25288338 |
Appl. No.: |
09/842829 |
Filed: |
April 27, 2001 |
Current U.S.
Class: |
473/357 |
Current CPC
Class: |
A63B 37/0049 20130101;
A63B 37/0064 20130101; A63B 37/0003 20130101; A63B 2037/087
20130101; A63B 37/0076 20130101; A63B 37/0045 20130101 |
Class at
Publication: |
473/357 |
International
Class: |
A63B 037/06 |
Claims
What is claimed is:
1. A golf ball having three or more concentrically disposed layers,
which comprises: a core of at least one layer comprising at least
one resilient elastomeric material; a hoop-stress layer comprising
at least one hoop-stress material having a tensile elastic modulus
of at least about 10,000 kpsi wound or wrapped about the core; and
an outermost thermoset material of at least one layer disposed
about the hoop-stress layer and having a thickness of greater than
about 0.065 inches and a dimpled outer surface.
2 The golf ball of claim 1, wherein the core comprises
polybutadiene.
3 The golf ball of claim 1, wherein the at least one hoop-stress
material comprises a wire, thread, or filament.
4 The golf ball of claim 1, wherein the at least one hoop-stress
material is comprises a continuous strand of diameter ranging from
about 0.004 to 0.04 inches.
5 The golf ball of claim 1, wherein the at least one hoop-stress
material comprises glass, aromatic polyamids, carbon, metals, shape
memory alloys, natural fibers, or a combination thereof.
6 The golf ball of claim 5, wherein the at least one hoop-stress
material is wound or wrapped in a criss-cross, basket weave, or
open pattern about the core.
7 The golf ball of claim 6, wherein the at least one hoop-stress
material comprises a plurality of braided elements.
8 The golf ball of claim 1, wherein the at least one hoop-stress
material has a tensile elastic modulus of at least about 20,000
kpsi.
9 The golf ball of claim 1, wherein the at least one layer of an
outermost thermoset material is formed from a material comprising
at least one of polybutadiene, natural rubber, styrene butadiene
rubber, isoprene, or mixtures thereof.
10 The golf ball of claim 1, wherein the at least one layer of an
outermost thermoset material comprises urethane.
11 The golf ball of claim 1, wherein the at least one layer of an
outermost thermoset material has a thickness of greater than about
0.065 inches.
12 The golf ball of claim 11, wherein the at least one layer of an
outermost thermoset material has a thickness of greater than about
0.08 inches.
13 The golf ball of claim 12, wherein the at least one layer of an
outermost thermoset material has a thickness of greater than about
0.1 inches.
14 The golf ball of claim 1, wherein the at least one layer of an
outermost thermoset material has a hardness of about 10 to 90 Shore
D.
15 The golf ball of claim 1, wherein the at least one layer of an
outermost thermoset material comprises an abrasion resistant
material.
16 The golf ball of claim 1, wherein the golf ball further
comprises a second resilient elastomeric material of at least one
layer disposed between the hoop-stress layer and the outermost
thermoset material.
17 The golf ball of claim 1, wherein the first resilient
elastomeric material and the outermost thermoset material each
comprise polybutadiene.
18 The golf ball of claim 17, wherein the polybutadiene is the
same.
19 A golf ball of four or more concentrically disposed layers,
which comprises: a core of at least one layer comprising a
resilient elastomeric material; a hoop-stress layer comprising at
least one wound material, having a tensile elastic modulus of at
least about 10,000 kpsi, disposed about the core, wherein the at
least one wound material forming the hoop-stress layer has a first
cross-sectional area and is coated with a binding material layer to
create a second cross-sectional area greater than the first; and an
outermost thermoset material of at least one layer, having a
dimpled outer surface, disposed about the binding material
layer.
20 The golf ball of claim 19, wherein the at least one wound
material has tensile elastic modulus of at least about 20,000
kpsi.
21 The golf ball of claim 19, wherein the at least one wound
material is a continuous strand of diameter ranging from about
0.004 to about 0.04 inches.
22 The golf ball of claim 19, wherein the second cross-sectional
area is at least about 5 percent larger than the first
cross-sectional area.
23 The golf ball of claim 19, wherein the binding material
comprises at least one of thermoplastic polyvinyl butyral,
thermoplastic epoxy, thermoplastic polyester phenolic,
thermoplastic polyamide, thermosetting adhesive epoxy,
thermoplastic polyamideimide, or combinations thereof.
24 The golf ball of claim 19, wherein the at least one layer of an
outermost thermoset material comprises at least one of
polybutadiene, natural rubber, and styrene butadiene rubber,
isoprene, or mixtures thereof.
25 The golf ball of claim 19, wherein the at least one layer of an
outermost thermoset material has a thickness of greater than about
0.08 inches.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to golf balls, and more
specifically, to a golf ball having a hoop-stress layer within a
layered rubber construction. In particular, it is directed to a
golf ball having multiple layers including a center of at least one
layer of a resilient elastomeric material, a hoop-stress layer
including at least one material with a tensile elastic modulus of
at least about 10,000 kpsi, and an outermost layer of a
thermosetting material. The golf balls of the present invention can
provide decreased spin and improved resiliency for better distance,
as well as maintaining the "soft" feel of a traditional wound
ball.
BACKGROUND OF THE INVENTION
[0002] Until recently, golf balls were typically divided into two
general types or groups: 1) two piece balls and 2) wound balls
(also known as three piece balls). The difference in play
characteristics resulting from these different types of
constructions can be quite significant.
[0003] Balls having a two piece construction are generally most
popular with the recreational golfer because they provide a very
durable ball while also providing maximum distance. Two piece balls
are made with a single solid core, usually formed of a crosslinked
rubber, which is encased by a cover material. Typically the solid
core is made of polybutadiene which is chemically crosslinked with
zinc diacrylate and/or similar crosslinking agents. The cover
comprises tough, cut-proof blends of one or more materials known as
ionomers such as SURLYN.RTM., which are resins sold commercially by
DuPont or IOTEK.RTM. which is sold commercially by Exxon.
[0004] The combination of the above-described core and cover
materials provides a "hard" covered ball that is resistant to
cutting and other damage caused by striking the ball with a golf
club. Further, such a combination imparts a high initial velocity
to the ball which results in increased distance. Due to their
hardness however, these balls have a relatively low spin rate which
makes them difficult to control, particularly on shorter approach
shots. As such, these types of balls are generally considered to be
"distance" balls. Because these materials are very rigid, many two
piece balls have a hard "feel" when struck with a club. Softer
cover materials such as balata and softer ionomers in some
instances, have been employed in two piece construction balls in
order to provide improved "feel" and increased spin rates.
[0005] Wound balls typically have either a solid rubber or fluid
center around which many yards of a tensioned elastic thread,
typically polyisoprene, are wrapped to form a wound core. The wound
core is then covered with a durable cover material such as a
SURLYN.RTM., or similar material, or a softer cover such as balata.
A wound material layer differs from a solid layer in that the wound
layer is often able to more readily elongate and compress in a
direction lateral to the impacting force. For this reason, wound
golf balls have a tendency to more easily compress at impact and
have more spin, as compared to a solid golf ball (Dalton, Golf and
Science III, 1999), which enables a skilled golfer to have more
control over the ball's flight. In particular, it is desirable that
a golfer be able to impart back spin to a golf ball for purposes of
controlling its flight and controlling the action of the ball upon
landing on the ground. For example, substantial back spin will make
the ball stop once it strikes the landing surface instead of
bounding forward. The ability to impart back spin onto a golf ball
is related to the extent to which the golf ball cover deforms when
it is struck with a golf club. Because wound balls are
traditionally more deformable than conventional two piece balls, it
is easier to impart spin to wound balls. However, wound higher
spinning balls typically travel a shorter distance when struck as
compared to a two piece ball. Moreover, as a result of their more
complex structure, wound balls generally require a longer time to
manufacture and are more expensive to produce than a two piece
ball.
[0006] Therefore, golf ball manufacturers are continually searching
for new ways in which to provide golf balls that deliver the
maximum performance in terms of both distance and spin rate for
golfers of all skill levels.
[0007] Golf ball designs have been introduced which use multilayer
non-wound constructions in an effort to overcome some of the
undesirable aspects of conventional two piece balls and wound
balls, while maintaining the positive attributes of these golf
balls (including their increased initial velocity and distance).
These include double cover designs with solid, single member cores;
dual core designs with two core members and a single cover layer;
and balls with multiple core and/or multiple cover layers.
[0008] A number of patents have been issued directed towards
modifying the properties of a conventional two piece ball by
altering the typical single layer core and/or single cover layer
construction to provide a multilayer core and/or cover. The
inventions disclosed in these patents are directed towards
improving a variety of golf ball characteristics.
[0009] One technique suggested in the prior art to avoid the
problem of an overly hard stiff cover was disclosed in U.S. Pat.
No. 4,431,193 issued to Nesbitt. Rather than have a single layer
cover over the core, the cover would be molded in two layers: a
hard stiff inner layer of a high flexural modulus material that
provides significant hoop stress, surrounded by a soft, flexible
outer cover of a lower flexural modulus material of approximately
14 kpsi. Balls of this design have been sold bearing the Strata
name for some time, however, because of the inner layer thickness
of about 0.045 inches to 0.050 inches and the high flexural modulus
of greater than 50,000 psi, the golf balls have a hard feel to
which many golfers object.
[0010] U.S. Pat. No. 5,072,944 discloses a three-piece solid golf
ball having a center and outer layer which are prepared from a
rubber composition, preferably having a base rubber of
polybutadiene. This patent teaches that it is desirable that the
center core is softer than the outer layer, wherein the layers have
a hardness (Shore C) of 25-50 and 70-90 respectively.
[0011] U.S. Pat. No. 5,002,281 is directed towards a three-piece
solid golf ball which has an inner core having a hardness of 25-70
(Shore C) and an outer shell having a hardness of 80-95 (Shore C),
wherein the specific gravity of the inner core must be greater than
1.0, but less than or equal to that of the outer shell, which must
be less than 1.3.
[0012] Additionally, several patents have been issued which employ
a wound layer of high tensile elastic modulus material, thus
replacing the need for a cover providing the necessary hoop-stress
in a golf ball.
[0013] U.S. Pat. No. 5,713,801 issued to Aoyama teaches a method
for making a golf ball providing a core of solid resilient
material, winding a high elastic modulus fiber on the core to
create a first wound layer to form a "hoop-stress layer," and
molding an outer layer of resilient material about the first wound
layer. The core in the above method and apparatus may also be made
of a center wound with a low modulus fiber and provided with an
initial tension. The preferred cover materials are ionomer and
balata.
[0014] U.S. Pat. No. 5,913,736 issued to Maehara et al. builds upon
Aoyama to describe a hoop-stress layer made of a shape memory alloy
(Ti--Ni) wound around a core so as to provide a shaped memory alloy
layer.
SUMMARY OF THE INVENTION
[0015] The golf ball of the present invention has three or more
concentrically disposed layers, including: a core, preferably
polybutadiene, of at least one layer formed of at least one
resilient elastomeric material; a hoop-stress layer including at
least one material, preferably wire, thread, or filament, under a
tensile elastic modulus of at least about 10,000 kpsi, preferably
at least about 20,000 kpsi, wound or wrapped about the core; and an
outermost thermoset material of at least one layer disposed about
the hoop-stress layer and having a thickness of greater than about
0.065 inches.
[0016] The material forming the hoop-stress layer is preferably a
continuous strand of diameter ranging from about 0.004 to 0.04
inches. The material can be glass, aromatic polyamids, carbon,
metals, shape memory alloys, natural fibers, or a combination
thereof and can be wound or wrapped in a criss-cross, basket weave,
or open pattern about the core. When wound or wrapped, the material
can include a plurality of braided elements.
[0017] The outermost thermoset material includes at least one of
polybutadiene, natural rubber, styrene butadiene rubber, isoprene,
or mixtures thereof and a hardness from about 10 to 90 Shore D. In
one embodiment, the outermost thermoset material includes
polybutadiene. The outermost layer can have a thickness of 0.065
inches, preferably 0.08 inches, and most preferably 0.1 inches. The
outermost layer can include an abrasion resistant material.
[0018] In one embodiment, the golf ball further includes a second
resilient elastomeric material of at least one layer disposed
between the hoop-stress layer and the outermost thermoset
material.
[0019] The first resilient elastomeric material and the outermost
thermoset material can each comprise polybutadiene. In one
embodiment, the polybutadiene used in the first resilient
elastomeric material and the outermost thermoset material is the
same.
[0020] Another embodiment of the invention is a golf ball having
four or more concentrically disposed layers, including: a core of
at least one layer formed from a resilient elastomeric material; an
outermost thermoset material of at least one layer, having a
thickness greater than about 0.065 inches, preferably greater than
about 0.08 inches, disposed about the second resilient elastomeric
material of at least one layer; and hoop-stress layer formed from
at least one wound material with a tensile elastic modulus of at
least about 10,000 kpsi, preferably at least about 20,000 kpsi,
disposed between the core and the outermost thermoset material,
wherein the at least one material forming the hoop-stress layer has
a first cross-sectional area and is coated with a binding material
layer to create a second cross-sectional area greater than the
first.
[0021] In this aspect of the invention, the material forming the
hoop-stress layer can be a continuous strand of diameter ranging
from about 0.004 to about 0.04 inches.
[0022] The binding material can include at least one of
thermoplastic polyvinyl butyral, thermoplastic epoxy, thermoplastic
polyester phenolic, thermoplastic polyamide, thermosetting adhesive
epoxy, thermoplastic polyamide-imide, or combinations thereof. The
second cross-sectional area is preferably at least about 5 percent
larger than the first cross-sectional area.
[0023] The outermost thermoset material includes at least one of
polybutadiene, natural rubber, and styrene butadiene rubber,
isoprene, or mixtures thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Further features and advantages of the invention can be
ascertained from the following detailed description which is
provided in connection with the attached drawings, wherein:
[0025] FIG. 1 illustrates a cross-section of a multilayer golf ball
with at least one center resilient elastomeric layer and a
hoop-stress layer in accordance with the present invention;
[0026] FIG. 2 illustrates a cross-section of a multilayer golf ball
with a plurality of center resilient elastomeric layers and a
hoop-stress layer disposed therebetween in accordance with an
embodiment of the present invention;
[0027] FIG. 3 illustrates a cross-section of a multilayer golf ball
with a hoop-stress layer and a binding material in accordance with
an embodiment of the present invention;
DEFINITIONS
[0028] The term "about," as used herein in connection with one or
more numbers or numerical ranges, should be understood to refer to
all such numbers, including all numbers in a range.
[0029] As used herein, the term "thermoset" material refers to an
irreversible, solid polymer that is the product of the reaction of
two or more prepolymer precursor materials.
[0030] As used herein, the term "multilayer" means at least three
layers and includes balls with at least one center layer, a
hoop-stress layer, and at least one outermost layer.
[0031] As used herein, the term "fluid" includes a liquid, a paste,
a gel, a gas, or any combination thereof.
[0032] As used herein, "cis-to-trans catalyst," means any component
or a combination thereof that will convert at least a portion of
cis-isomers to trans-isomers in polybutadiene at a given
temperature.
[0033] As used herein, the term "parts per hundred", also known as
"phr", is defined as the number of parts by weight of a particular
component present in a mixture, relative to 100 parts by weight of
the total polymer component. Mathematically, this can be expressed
as the weight of an ingredient divided by the total weight of the
polymer, multiplied by a factor of 100.
[0034] As used herein, the term "molecular weight" is defined as
the absolute eight average molecular weight. The molecular weight
is determined by the following method: approximately 20 mg of
polymer is dissolved in 10 mL of tetrahydrofuran ("THF"), which may
take a few days at room temperature depending on the polymer's
molecular weight and distribution. One liter of THF is filtered and
degassed before being placed in a high-performance liquid
chromatography ("HPLC") reservoir. The flow rate of the HPLC is set
to 1 mL/min through a Viscogel column. This non-shedding, mixed
bed, column model GMHHR-H, which has an ID of 7.8 mm and 300 mm
long is available from Viscotek Corp. of Houston, Tex. The THF flow
rate is set to 1 mL/min for at least one hour before sample
analysis is begun or until stable detector baselines are achieved.
During this purging of the column and detector, the internal
temperature of the Viscotek TDA Model 300 triple detector should be
set to 40.degree. C. This detector is also available from Viscotek
Corp. The three detectors (i.e., Refractive Index, Differential
Pressure, and Light Scattering) and the column should be brought to
thermal equilibrium, and the detectors should be purged and zeroed,
to prepare the system for calibration according to the instructions
provided with this equipment. A 100-.mu.L aliquot of sample
solution can then be injected into the equipment and the molecular
weight of each sample can be calculated with the Viscotek's triple
detector software. When the molecular weight of the polybutadiene
material is measured, a dn/dc of 0.130 should always be used. It
should be understood that this equipment and these methods provide
the molecular weight numbers described and claimed herein, and that
other equipment or methods will not necessarily provide equivalent
values as used herein.
[0035] As used herein the term "resilience index" is defined as the
difference in loss tangent measured at 10 cpm and 1000 cpm divided
by 990 (the frequency span) multiplied by 100,000 (for
normalization and unit convenience). The loss tangent is measured
using an RPA 2000 manufactured by Alpha Technologies of Akron,
Ohio. The RPA 2000 is set to sweep from 2.5 to 1000 cpm at a
temperature of 100.degree. C. using an arc of 0.5 degrees. An
average of six loss tangent measurements were acquired at each
frequency and the average is used in calculation of the resilience
index. The computation of resilience index is as follows:
Resilience Index=100,000.multidot.[(loss tangent@10 cpm)-(loss
tangent@1000 cpm)]/990
[0036] As used herein, the term "substantially free" means less
than about 5 weight percent, preferably less than about 3 weight
percent, more preferably less than about 1 weight percent, and most
preferably less than about 0.01 weight percent.
DETAILED DESCRIPTION OF THE INVENTION
[0037] It has now been discovered that the use of a hoop-stress
layer in combination with an all rubber golf ball, according to the
present invention, thereby permits a golf ball construction having
no traditional cover without sacrificing the performance benefits
of a typical "hard" cover ball formed of one or more thermoplastic
materials.
[0038] Without being limited to any particular theory, it is
believed that with low club head speed and high loft shots such as
those made with an high-numbered iron or a sand wedge, a ball's
surface hardness has a greater influence on the ball's flight
characteristics than the ball's overall construction. Thus, all
other parameters being equal, a ball with a softer outermost layer
will have a higher spin rate than one with a harder surface when
struck with an iron or a wedge, regardless of the ball's overall
construction. In contrast, when a golf ball is struck with a high
club head speed and a low loft angle, such as that of a driver, the
overall construction of the ball has a greater influence on the
ball's flight characteristics than does the surface hardness.
[0039] The present invention advantageously provides a golf ball
that returns to shape post-impact thus preventing permanent
deformation of the ball, even in the absence of a traditional
cover. In most conventional golf balls, one or more layers of a
cover of such balls is stiffer than the core materials.
Conventional covers provide durability, as well as providing
protection for the inner materials. In contrast, the present
invention uses a hoop-stress layer formed of a wound, high tensile
elastic modulus material, such as a thread, fiber, filament, or
wire, to provide the necessary hoop-stress in a golf ball, thus
permitting construction of a golf ball with different types of
cover compositions. This wound high tensile elastic modulus layer
can be incorporated within one or more layers of a solid multilayer
core, wherein the innermost layer(s) of the core are very soft and
subject to high deflections upon impact with a golf club, or simply
be wound or wrapped around a single layer core. In addition, a
binding material can coat the hoop-stress layer so that the layer
will remain properly positioned around the core or core of the golf
ball.
[0040] The golf ball of the invention is believed to provide a
further benefit for a golfer's short game. The spin of a ball after
being struck with a large force, such as with a driver, is
controlled by the relationship between the softness (flexibility)
of the outermost layer and the compressibility of the core of the
golf ball. When the impact force is low, such as in the short game,
the resulting spin of a golf ball is controlled almost entirely by
surface (outermost layer) hardness. A softer outermost layer is
desired by golfers to improve short game spin, however, it also
increases driver spin and decreases distance. To some extent,
softening the core can reduce the driver spin of soft-covered
balls, but if both the outermost layer and the core are too soft,
the golf ball loses resiliency and the resulting initial velocity
and distance that are also desired in a golf ball. Therefore, golf
ball manufacturers are challenged with making a soft outermost
layer golf ball with low driver spin, which the present invention
advantageously provides.
[0041] Thus, improved golf balls can be prepared according to the
invention by: (a) providing a resilient elastomeric core of at
least one layer; (b) winding or wrapping a hoop-stress layer of
high tensile elastic modulus material about the core; (c)
surrounding the hoop-stress layer with at least one outermost layer
formed including a thermoset material; and optionally, (d) coating
the material with a first cross-sectional area forming the
hoop-stress layer to create a second cross-sectional area greater
than the first before applying the outermost layer. The hoop-stress
layer and the thickness of the outermost thermoset layer are
critical to the performance of the golf balls of the present
invention.
[0042] In one embodiment, shown in FIG. 1, a unitary golf ball core
100 is surrounded by a hoop-stress layer 105 of a high tensile
elastic modulus filament of at least 10,000 kpsi. This hoop-stress
layer is surrounded by at least one outermost layer including a
thermoset material 110.
[0043] In a second embodiment, shown in FIG. 2, a golf ball core
includes a core 100 surrounded by a hoop-stress layer 105 of a high
tensile elastic modulus of at least 10,000 kpsi. This hoop-stress
layer is surrounded by an intermediate resilient elastomeric
material 100A, which in turn is protected by an outermost thermoset
material layer 110. In an alternate second embodiment, the core is
at least two layers 100 and 105, e.g., two solid layers or a fluid
center contained by an encapsulating shell. The hoop-stress layer
100A surrounds the core layers and a thermoset layer 110 is applied
to the hoop-stress layer to form a golf ball.
[0044] In a third embodiment of the invention, shown in FIG. 3, the
filament forming the hoop-stress layer is coated with a binding
material to ensure repeatable proper positioning of the hoop-stress
layer during manufacturing. A hoop-stress layer 105 is wound or
wrapped about the core 100, or in an embodiment not shown, the
hoop-stress layer is situated between an innermost core layer and
an intermediate resilient elastomeric material. The filament of
hoop-stress layer 105 is coated with a binding material 105A that
will adhere to the core and itself when activated. In another
embodiment (not shown), the binding material coats a portion of the
filament without forming a separate layer. An outermost thermoset
material of at least one layer 110 surrounds the inner components
of the ball.
[0045] The Cores
[0046] The golf ball cores of the present invention may comprise
any of a variety of constructions. For example, the core of the
golf ball may comprise a conventional core surrounded by a
hoop-stress layer disposed between the core and the outermost
thermoset layer. The core may be a single layer or may include a
plurality of layers.
[0047] The solid core is typically a homogenous mass of a resilient
material having a base rubber, a crosslinking agent, a filler, and
a co-crosslinking or initiator agent. The base rubber typically
includes one or more natural or synthetic rubbers. A preferred base
rubber is 1,4-polybutadiene having a cis-structure of at least 40%.
If desired, the polybutadiene can also be mixed with other
elastomers known in the art such as natural rubber, polyisoprene
rubber and/or styrene-butadiene rubber in order to modify the
properties of the core.
[0048] Preferred commercial sources of polybutadiene include Shell
1220 manufactured by Shell Chemical, Neocis BR40 and BR60
manufactured by Enichem Elastomers, Ubepol BRI 50 and 360
manufactured by Ube Industries, Ltd., CB23 manufactured by Bayer
Corporation of Akron, Ohio, and BUDENE 1207G, manufactured by
Goodyear. If desired, the polybutadiene can also be mixed with
other elastomers known in the art, such as natural rubber, styrene
butadiene, and/or isoprene in order to further modify the
properties of the material. When a mixture of elastomers is used,
the amounts of other constituents in the core composition are
generally based on 100 parts by weight of the total elastomer
mixture.
[0049] In one embodiment, the resilience index of the core is
greater than about 40, preferably greater than about 45. In one
preferred embodiment, the resilience index of the core is greater
than about 50. The core compression can thus be reduced, thereby
decreasing the overall spin rate of the ball without a significant
loss in golf ball initial velocity. An exemplary finished ball
velocity according to the present invention can advantageously be
about 253.5 to 254.5 ft/s. These correspond to CORs of 0.812 and
0.818 respectively.
[0050] The crosslinking agent includes a metal salt of an
unsaturated fatty acid such as a zinc salt or a magnesium salt of
an unsaturated fatty acid having 3 to 8 carbon atoms such as
acrylic or methacrylic acid. Suitable cross linking agents include
metal salt diacrylates, dimethacrylates and monomethacrylates
wherein the metal is magnesium, calcium, zinc, aluminum, sodium,
lithium or nickel.
[0051] Metal salt diacrylates, dimethacrylates, and
monomethacrylates suitable for use in this invention include those
wherein the metal is magnesium, calcium, zinc, aluminum, sodium,
lithium or nickel. Zinc diacrylate is preferred, because it
provides golf balls with a high initial velocity in the USGA test.
The zinc diacrylate can be of various grades of purity. For the
purposes of this invention, the lower the quantity of zinc stearate
present in the zinc diacrylate the higher the zinc diacrylate
purity. Zinc diacrylate containing about 1 to 10 percent zinc
stearate is preferable. More preferable is zinc diacrylate
containing about 4 to 8 percent zinc stearate. Preferred
commercially available zinc diacrylates include those from Rockland
React-Rite and Sartomer. The preferred concentrations of zinc
diacrylate that can be used are about 20 to 50 phr based upon 100
parts of polybutadiene or alternately, polybutadiene with a mixture
of other elastomers.
[0052] Free radical initiators are used to promote cross-linking of
the metal salt diacrylate, dimethacrylate, or monomethacrylate and
the polybutadiene. Suitable free radical initiators for use in the
invention include, but are not limited to, peroxide compounds.
Exemplary peroxides include dicumyl peroxide, 1,1 -di
(t-butylperoxy) 3,3,5-trimethyl cyclohexane, a-a bis
(t-butylperoxy) diisopropylbenzene, 2,5-dimethyl-2,5 di
(t-butylperoxy) hexane, or di-t-butyl peroxide, and mixtures
thereof. Other useful initiators will be readily apparent to one of
ordinary skill in the art without any need for experimentation. The
initiator(s) at 100% activity are preferably added in an amount
ranging between about 0.05 and 2.5 phr based upon 100 parts of
butadiene, or butadiene mixed with one or more other elastomers.
More preferably, the amount of initiator added ranges between about
0.15 and 2 phr and most preferably between about 0.25 and 1.5
phr.
[0053] Many golf balls use fillers added to the elastomeric
composition in the cores to adjust the density and/or specific
gravity of the core. In a preferred embodiment, the golf balls of
the present invention are substantially free of filler, or even
completely free of added filler. As used herein, the term "fillers"
includes any compound or composition that can be used to vary the
density or other properties of a layer or portion of a golf ball.
If needed, fillers useful in the golf ball according to the present
invention include, for example, precipitated hydrated silica; clay;
talc; glass fibers; aramid fibers; mica; calcium metasilicate;
barium sulfate; zinc sulfide; lithopone; silicates; silicon
carbide; diatomaceous earth; carbonates such as calcium carbonate
and magnesium carbonate; metals such as titanium, tungsten,
aluminum, bismuth, nickel, molybdenum, iron, copper, boron, cobalt,
beryllium, zinc, and tin; metal alloys such as steel, brass,
bronze, boron carbide whiskers, and tungsten carbide whiskers;
metal oxides such as zinc oxide, iron oxide, aluminum oxide,
titanium oxide, magnesium oxide, and zirconium oxide; particulate
carbonaceous materials such as graphite, carbon black, cotton
flock, natural bitumen, cellulose flock, and leather fiber; micro
balloons such as glass and ceramic; fly ash; and combinations
thereof. The amount and type of filler utilized is governed by the
amount and weight of other ingredients in the composition, since a
maximum golf ball weight of 45.93 g (1.62 ounces) has been
established by the United States Golf Association (USGA).
Appropriate fillers generally used have a specific gravity from
about 2 to 20. In one preferred embodiment, a filler having a
specific gravity of about 12 to 20 can be included.
[0054] In one embodiment, the core is at least two layers, e.g. two
solid layers or a fluid center contained by an encapsulating shell.
The hoop-stress layer surrounds the core layers and a thermoset
layer having a thickness greater than about 0.065 inches is formed
around the hoop-stress layer to form a golf ball.
[0055] The cores employed in the golf balls of the present
invention preferably have a diameter of about 1 inch to 1.6 inches,
more preferably about 1.1 inches to 1.5 inches.
[0056] The cores of the present invention can be made by any
suitable process available in the art. For example, the solid cores
can be either injection or compression molded.
[0057] The Hoop-Stress Layer
[0058] The hoop-stress layer of the present invention has a tensile
modulus of at least about 10,000 kpsi and is formed of a high
tensile "filament", which can be a filament, fiber, thread, or
wire, preferably including glass, aromatic polyamids, carbon,
metals, shape memory alloys, or natural fibers, or a combination or
blend thereof. The hoop-stress layer is wound or wrapped about the
core of one or more layers. In a more preferred embodiment, the
hoop-stress layer has a tensile modulus of at least about 20,000
kpsi. If a hoop-stress layer is created using a high density
material, such as a metal, the ball will typically have an
increased moment of inertia, and thus will tend to spin less when
struck with a golf club and yet retain its spin longer during
flight. The use of high density materials in the hoop-stress layer
can advantageously permit the fillers from other components of the
golf ball to be reduced or removed while keeping the overall golf
ball weight constant. Specifically, removing fillers from
elastomeric components such as the resilient elastomeric material
used as another layer of the ball can soften and increase
resilience of the components and even the ball as a whole.
[0059] Any suitable winding or wrapping method known to those of
ordinary skill in the art can be used to form the hoop-stress
layer. Preferably, the hoop-stress layer is created winding strands
in a criss-cross, basket weave, or open pattern, which requires
fewer wraps than a great circle pattern and a less dense
application to obtain spherical symmetry. The criss-cross pattern
typically employs a fairly large lateral rotation during winding.
One such suitable method is described in U.S. Pat. No. 4,938,471 to
Nomura et al., wherein at least 8 turns of every ten turns of
strands around the core have a crossing angle between two
consecutive turns in the range of 12.degree. to 45.degree.. The
hoop-stress layer can include multiple strands that are braided, or
otherwise entwined, during the winding or wrapping process.
[0060] In one embodiment, a binding material preferably coats the
material which forms the hoop-stress layer, such that the
cross-sectional area of the coated hoop-stress layer is greater
than the cross-sectional area of the wound layer alone. The binding
material preferably causes the strands of the hoop-stress layer to
swell so as to increase the cross-sectional area of each thread.
This can advantageously permit repeatable proper positioning of the
hoop-stress layer around the core or core of the golf ball. In a
preferred embodiment, the binding material increases the
cross-sectional area of the hoop-stress layer by at least about
five (5) percent. In a preferred embodiment, the cross-sectional
area can be increased by at least about ten (10) percent. The
binding material can include one or more thermoset or thermoplastic
materials. Preferably, the binding material includes thermoplastic
polyvinyl butyral, thermoplastic epoxy, thermoplastic polyester
phenolic, thermoplastic polyamide, thermosetting adhesive epoxy,
thermoplastic polyamide-imide, or a combination thereof. The
binding material can be activated, for example, by heat, pressure,
chemical or photo-activation, before, during, or after the winding
process.
[0061] The hoop-stress layers include one or more threads, but are
preferably made of a single continuous strand with a diameter
ranging from about 0.004 inches to 0.04 inches. The hoop-stress
thread preferably includes one or more high specific gravity
alloys.
[0062] Examples of suitable high specific gravity alloys are alloys
that have specific gravities greater than about 7.6, which include
steel, brass, bronze, copper, nickel, lead, titanium, gold, silver,
and platinum. Exemplary alloys include steel, brass, and bronze as
they provide the best combination of tensile strength (greater than
about 250 N/mm.sup.2) and high specific gravity (preferably ranging
from about 7.6 to 10). While gold, silver, and platinum have higher
specific gravities than other suitable alloys, they tend to be more
expensive; copper and nickel have similar specific gravities as the
exemplary alloys, but do not tend to provide comparable strength;
and titanium is strong, but tends to have a lower specific gravity
than steel.
[0063] The hoop-stress layers employed in the golf balls of the
present invention preferably have a thickness from about 0.01
inches to 0.1 inches, more preferably about 0.02 inches to 0.08
inches. In one exemplary embodiment, the hoop-stress layer has a
thickness of about 0.04 inches. The outer diameter of the
hoop-stress layer is preferably from about 1.3 to about 1.63
inches.
[0064] The Outermost Thermoset Layer
[0065] The outermost thermoset layer is formed from a relatively
soft thermoset material in order to replicate the soft feel and
high spin play characteristics of a balata ball when the balls of
the present invention are used for pitch and other "short game"
shots. In particular, the outermost thermoset layer should have a
Shore D hardness of from about 10 to 90, preferably from about 30
to 80, and most preferably from about 40 to 75. Additionally, the
materials of the outermost thermoset layer must have a sufficient
abrasion and cut resistance in order to be suitable for use as a
golf ball cover.
[0066] The outermost thermoset layer of the present invention can
include any suitable thermoset material. The preferred materials
for the outermost thermoset layer include, but are not limited to,
polybutadiene, natural rubber, styrene butadiene rubber, isoprene,
or combinations thereof. In one more preferred embodiment, the
outermost layer includes one or more of the polybutadienes
described herein for use in the core.
[0067] If the outermost thermoset layer is too thick, this layer
will contribute to the in-flight characteristics related to the
overall construction of the ball and not the surface properties. If
the outermost thermoset layer is too thin, however, it may not be
durable enough to withstand repeated impacts by the golfer's clubs.
Specifically, it has been determined that the outer cover layer
should have a thickness of greater than about 0.065 inches,
preferably greater than about 0.08 inches, and more preferably
greater than about 01 inches.
[0068] The multi-layer golf ball of the invention can have an
overall diameter of any size. Although the United States Golf
Association specifications limit the minimum size of a competition
golf ball to 1.68 inches in diameter or more, there is no
specification as to the maximum diameter. Moreover, golf balls of
any size can be used for recreational play. The preferred diameter
of the present golf balls is from about 1.68 inches to 1.8 inches.
The more preferred diameter is from about 1.68 inches to 1.76
inches. The most preferred diameter is about 1.68 inches to 1.7
inches.
[0069] It is to be understood that the invention is not to be
limited to the exact configuration as illustrated and described
herein. For example, it should be apparent that a variety of
materials would be suitable for use in the composition or method of
making the golf equipment according to the Detailed Description of
the Preferred Embodiments. Accordingly, all expedient modifications
readily attainable by one of ordinary skill in the art from the
disclosure set forth herein, or by routine experimentation
therefrom, are deemed to be within the spirit and scope of the
invention as defined by the appended claims.
* * * * *