U.S. patent application number 14/982677 was filed with the patent office on 2017-06-29 for golf balls having multi-layered cores with heat-activated foam center.
This patent application is currently assigned to Acushnet Company. The applicant listed for this patent is Acushnet Company. Invention is credited to Mark L. Binette, Brian Comeau, Douglas S. Goguen, Derek A. Ladd, Michael Michalewich, Shawn Ricci, Michael J. Sullivan.
Application Number | 20170182369 14/982677 |
Document ID | / |
Family ID | 59088201 |
Filed Date | 2017-06-29 |
United States Patent
Application |
20170182369 |
Kind Code |
A1 |
Binette; Mark L. ; et
al. |
June 29, 2017 |
GOLF BALLS HAVING MULTI-LAYERED CORES WITH HEAT-ACTIVATED FOAM
CENTER
Abstract
Multi-layered, golf balls having a core made of a foamed
composition are provided. The core preferably has a foam inner core
(center) and surrounding thermoset or thermoplastic outer core
layer. Preferably, a polyurethane foam composition comprising
secondary blowing agents that are activated by heat is used to form
the foam center. Non-foamed thermoset materials such as
polybutadiene rubber may be used to form the outer core layer. The
core layers have different hardness gradients and specific gravity
values. The foam cores have good resiliency, thermal stability, and
durability over a wide temperature range. The ball further includes
a cover that may be multi-layered.
Inventors: |
Binette; Mark L.;
(Mattapoisett, MA) ; Sullivan; Michael J.; (Old
Lyme, CT) ; Ladd; Derek A.; (Acushnet, MA) ;
Comeau; Brian; (Berkley, MA) ; Michalewich;
Michael; (Norton, MA) ; Ricci; Shawn; (New
Bedford, MA) ; Goguen; Douglas S.; (New Bedford,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Acushnet Company |
Fairhaven |
MA |
US |
|
|
Assignee: |
Acushnet Company
Fairhaven
MA
|
Family ID: |
59088201 |
Appl. No.: |
14/982677 |
Filed: |
December 29, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A63B 37/0064 20130101;
C08G 18/44 20130101; A63B 37/0091 20130101; A63B 37/0066 20130101;
A63B 37/0056 20130101; A63B 37/0075 20130101; A63B 37/0058
20130101; A63B 37/0063 20130101; C08G 18/42 20130101; C08G
2101/0083 20130101; A63B 37/0045 20130101; C08G 18/10 20130101;
A63B 37/0044 20130101; A63B 37/0043 20130101; C08G 2101/00
20130101; A63B 37/0062 20130101; A63B 37/0051 20130101; A63B
37/0078 20130101; A63B 37/0047 20130101; C08G 18/6204 20130101;
C08G 18/48 20130101; A63B 37/0039 20130101; A63B 37/0076 20130101;
A63B 45/00 20130101; A63B 37/0092 20130101; A63B 37/0094
20130101 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Claims
1. A golf ball, comprising a core assembly and a cover, the core
assembly comprising: i) an inner core layer comprising a secondary
heat-activated foam composition, the inner core layer having a
diameter in the range of about 0.100 to about 1.100 inches and a
specific gravity (SG.sub.inner) and a center hardness (H.sub.inner
core center); and ii) an outer core layer comprising a non-foamed
thermoset rubber composition, the outer core layer being disposed
about the inner core layer and having a thickness in the range of
about 0.100 to about 0.750 inches, and a specific gravity
(SG.sub.outer) and an outer surface hardness (H.sub.outer surface
of OC), wherein the SG.sub.outer, is greater than the SG.sub.inner,
and the H.sub.inner core center is in the range of about 10 to
about 60 Shore C and the H.sub.outer surface of OC is in the range
of about 65 to about 96 Shore C to provide a positive hardness
gradient across the core assembly.
2. The golf ball of claim 1, wherein the secondary heat-activated
foam composition comprises primary and secondary chemical blowing
agents.
3. The golf ball of claim 2, wherein the primary blowing agent is
water and the secondary chemical blowing agent is selected from the
group consisting of azo, nitroso, hydrazine, carbazide, and
hydrogen carbonate compounds, and mixtures thereof.
4. The golf ball of claim 1, wherein the secondary blowing agent is
selected from the group consisting of
4,4'-oxybis(benzenesulfonylhydrazide) and sodium hydrogen
carbonate.
5. The golf ball of claim 1, wherein the wherein the secondary
heat-activated foam composition further comprises expandable
gas-containing microspheres.
6. The core assembly of claim 1, wherein the inner core comprises a
foamed polyurethane composition.
7. The golf ball of claim 6, wherein the foamed polyurethane
composition is prepared by adding water and a secondary chemical
blowing agent to a mixture of polyisocyanate, polyol, and curing
agent compounds, surfactant, and catalyst, the water being added in
a sufficient amount to cause the mixture to foam.
8. The golf ball of claim 1, wherein the outer core layer comprises
at least one thermoset rubber material selected from the group
consisting of polybutadiene, ethylene-propylene rubber,
ethylene-propylene-diene rubber, polyisoprene, styrene-butadiene
rubber, polyalkenamers, butyl rubber, halobutyl rubber, polystyrene
elastomers, copolymers of isobutylene and p-alkylstyrene,
halogenated copolymers of isobutylene and p-alkylstyrene,
copolymers of butadiene with acrylonitrile, polychloroprene, alkyl
acrylate rubber, chlorinated isoprene rubber, acrylonitrile
chlorinated isoprene rubber, and mixtures thereof
9. The golf ball of claim 8, wherein the outer core layer comprises
a thermoset polybutadiene rubber composition.
10. The golf ball of claim 1, wherein the inner core layer has a
diameter in the range of about 0.100 to about 0.900 inches and a
specific gravity in the range of about 0.25 to about 1.25 g/cc.
11. The golf ball of claim 1, wherein the inner core layer has a
diameter in the range of about 0.400 to about 0.800 inches and a
specific gravity in the range of about 0.30 to about 0.95 g/cc.
12. The golf ball of claim 1, wherein the outer core layer has a
thickness in the range of about 0.250 to about 0.750 inches and a
specific gravity in the range of about 0.60 to about 2.90 g/cc.
13. The golf ball of claim 1, wherein the inner core layer has an
outer surface hardness (H.sub.inner core surface) and a center
hardness (H.sub.inner core center), the H.sub.inner core surface
being greater than the H.sub.inner core center to provide a
positive hardness gradient; and the outer core layer has an outer
surface hardness (H.sub.outer surface of OC) and a midpoint
hardness (H.sub.midpoint of OC), the H.sub.outer surface of OC
being greater than the (H.sub.midpoint of OC), to provide a
positive hardness gradient.
14. The golf ball of claim 13, wherein the H.sub.inner core center
is in the range of about 10 to about 48 Shore C and the H.sub.inner
core surface is in the range of about 24 to about 55 Shore C.
15. The golf ball of claim 13, wherein the H.sub.inner core center
is in the range of about 15 to about 80 Shore A and the H.sub.inner
core surface is in the range of about 20 to about 95 Shore A.
16. The golf ball of claim 13, wherein the H.sub.midpoint of OC is
in the range of about 40 to about 87 Shore C and the H.sub.outer
surface of OC is in the range of about 72 to about 95 Shore C.
17. The golf ball of claim 1, wherein the inner core layer has an
outer surface hardness (H.sub.inner core surface) and a center
hardness (H.sub.inner core center), the H.sub.inner core surface
being the same or less than the H.sub.inner core center to provide
a zero or negative hardness gradient; and the outer core layer has
an outer surface hardness (H.sub.outer surface of OC) and a
midpoint hardness (H.sub.midpoint of OC), the H.sub.outer surface
of OC being greater than the (H.sub.midpoint of OC), to provide a
positive hardness gradient.
18. The golf ball of claim 17, wherein the H.sub.inner core center
is in the range of about 10 to about 60 Shore C and the H.sub.inner
core surface is in the range of about 10 to about 55 Shore C.
19. The golf ball of claim 17, wherein the H.sub.inner core center
is in the range of about 15 to about 80 Shore A and the H.sub.inner
core surface is in the range of about 10 to about 75 Shore A.
20. The golf ball of claim 17, wherein the H.sub.midpoint of OC is
in the range of about 45 to about 85 Shore C and the H.sub.outer
surface of OC is in the range of about 72 to about 95 Shore C.
Description
BACKGROUND OF THE INVENTION
[0001] Field of the Invention
[0002] The present invention relates generally to multi-layered,
golf balls having a core made of a foamed composition.
Particularly, the dual-layered core has a foam inner core (center)
and surrounding thermoset or thermoplastic outer core layer.
Preferably, a polyurethane foam composition comprising secondary
blowing agents that are activated by heat is used to form the foam
center. The core layers have different hardness gradients and
specific gravity values. The ball further includes a cover having
at least one layer.
[0003] Brief Review of the Related Art
[0004] Both professional and amateur golfer use multi-piece, solid
golf balls today. Basically, a two-piece solid golf ball includes a
solid inner core protected by an outer cover. The inner core is
made of a natural or synthetic rubber such as polybutadiene,
styrene butadiene, or polyisoprene. The cover surrounds the inner
core and may be made of a variety of materials including, for
example, ethylene acid copolymer ionomers, polyamides, polyesters,
polyurethanes, and polyureas.
[0005] In recent years, three-piece, four-piece, and even
five-piece balls have become more popular. New manufacturing
technologies, lower material costs, and desirable performance
properties have contributed to these multi-piece balls becoming
more popular. Many golf balls used today have multi-layered cores
comprising an inner core and at least one surrounding outer core
layer. For example, the inner core may be made of a relatively soft
and resilient material, while the outer core may be made of a
harder and more rigid material. The "dual-core" sub-assembly is
encapsulated by a cover having at least one layer to provide a
final ball assembly. Different materials can be used to manufacture
the core and cover thus imparting desirable properties to the final
ball.
[0006] In general, dual-cores comprising an inner core (or center)
and a surrounding outer core layer are known in the industry. For
example, Sugimoto, U.S. Pat. No. 6,390,935 discloses a three-piece
golf ball comprising a core having a center and outer shell and a
cover disposed about the core. The specific gravity of the outer
shell is greater than the specific gravity of the center. The
center has a JIS-C hardness (X) at the center point thereof and a
JIS-C hardness (Y) at a surface thereof satisfying the equation:
(Y-X).gtoreq.8. The core structure (center and outer shell) has a
JIS-C hardness (Z) at a surface of 80 or greater. The cover has a
Shore D hardness of less than 60.
[0007] Endo, U.S. Pat. No. 6,520,872 discloses a three-piece golf
ball comprising a center, an intermediate layer formed over the
center, and a cover formed over the intermediate layer. The center
is preferably made of high-cis polybutadiene rubber; and the
intermediate and cover layers are preferably made of an ionomer
resin such as an ethylene acid copolymer.
[0008] Watanabe, U.S. Pat. No. 7,160,208 discloses a three-piece
golf ball comprising a rubber-based inner core; a rubber-based
outer core layer; and a polyurethane elastomer-based cover. The
inner core layer has a JIS-C hardness of 50 to 85; the outer core
layer has a JIS-C hardness of 70 to 90; and the cover has a Shore D
hardness of 46 to 55. Also, the inner core has a specific gravity
of more than 1.0, and the core outer layer has a specific gravity
equal to or greater than that of that of the inner core.
[0009] The core sub-structure located inside of the golf ball acts
as an engine or spring for the ball. Thus, the composition and
construction of the core is a key factor in determining the
resiliency and rebounding performance of the ball. In general, the
rebounding performance of the ball is determined by calculating its
initial velocity after being struck by the face of the golf club
and its outgoing velocity after making impact with a hard surface.
More particularly, the "Coefficient of Restitution" or "COR" of a
golf ball refers to the ratio of a ball's rebound velocity to its
initial incoming velocity when the ball is fired out of an air
cannon into a rigid vertical plate. The COR for a golf ball is
written as a decimal value between zero and one. A golf ball may
have different COR values at different initial velocities. The
United States Golf Association (USGA) sets limits on the initial
velocity of the ball so one objective of golf ball manufacturers is
to maximize COR under such conditions. Balls with a higher rebound
velocity have a higher COR value. Such golf balls rebound faster,
retain more total energy when struck with a club, and have longer
flight distance versus balls with low COR values. These properties
are particularly important for long distance shots. For example,
balls having high resiliency and COR values tend to travel a
relatively far distance when struck by a driver club from a
tee.
[0010] The durability, spin rate, and feel of the ball also are
important properties. In general, the durability of the ball refers
to the impact-resistance of the ball. Balls having low durability
appear worn and damaged even when such balls are used only for
brief time periods. In some instances, the cover may be cracked or
torn. The spin rate refers to the ball's rate of rotation after it
is hit by a club. Balls having a relatively high spin rate are
advantageous for short distance shots made with irons and wedges.
Professional and highly skilled amateur golfers can place a back
spin more easily on such balls. This helps a player better control
the ball and improves shot accuracy and placement. By placing the
right amount of spin on the ball, the player can get the ball to
stop precisely on the green or place a fade on the ball during
approach shots. On the other hand, recreational players who cannot
intentionally control the spin of the ball when hitting it with a
club are less likely to use high spin balls. For such players, the
ball can spin sideways more easily and drift far-off the course,
especially if the ball is hooked or sliced. Meanwhile, the "feel"
of the ball generally refers to the sensation that a player
experiences when striking the ball with the club and it is a
difficult property to quantify. Most players prefer balls having a
soft feel, because the player experience a more natural and
comfortable sensation when their club face makes contact with these
balls. Balls having a softer feel are particularly desirable when
making short shots around the green, because the player senses more
with such balls. The feel of the ball primarily depends upon the
hardness and compression of the ball.
[0011] Manufacturers of golf balls are constantly looking to
different materials for improving the playing performance and other
properties of the ball. For example, golf balls containing cores
made from foam compositions are generally known in the industry.
Puckett and Cadorniga, U.S. Pat. Nos. 4,836,552 and 4,839,116
disclose one-piece, short distance golf balls made of a foam
composition comprising a thermoplastic polymer (ethylene acid
copolymer ionomer such as Surlyn.RTM.) and filler material
(microscopic glass bubbles). The density of the composition
increases from the center to the surface of the ball. Thus, the
ball has relatively dense outer skin and a cellular inner core.
According to the '552 and '116 Patents, by providing a short
distance golf ball, which will play approximately 50% of the
distance of a conventional golf ball, the land requirements for a
golf course can be reduced 67% to 50%.
[0012] Gentiluomo, U.S. Pat. No. 5,104,126 discloses a three-piece
golf ball (FIG. 2) containing a high density center (3) made of
steel, surrounded by an outer core (4) of low density resilient
syntactic foam composition, and encapsulated by an ethylene acid
copolymer ionomer (Surlyn.RTM.) cover (5). The '126 Patent defines
the syntactic foam as being a low density composition consisting of
granulated cork or hollow spheres of either phenolic, epoxy,
ceramic or glass, dispersed within a resilient elastomer.
[0013] Aoyama, U.S. Pat. Nos. 5,688,192 and 5,823,889 disclose a
golf ball containing a core, wherein the core comprising an inner
and outer portion, and a cover made of a material such as balata
rubber or ethylene acid copolymer ionomer. The core is made by
foaming, injecting a compressible material, gasses, blowing agents,
or gas-containing microspheres into polybutadiene or other core
material. According to the '889 Patent, polyurethane compositions
may be used. The compressible material, for example, gas-containing
compressible cells may be dispersed in a limited part of the core
so that the portion containing the compressible material has a
specific gravity of greater than 1.00. Alternatively, the
compressible material may be dispersed throughout the entire core.
In one embodiment, the core comprises an inner and outer portion.
In another embodiment, the core comprises inner and outer
layers.
[0014] Sullivan and Ladd, U.S. Pat. No. 6,688,991 discloses a golf
ball containing a low specific gravity core, optional intermediate
layer, and high specific gravity cover with Shore D hardness in the
range of about 40 to about 80. The core is preferably made from a
highly neutralized thermoplastic polymer such as ethylene acid
copolymer which has been foamed.
[0015] Nesbitt, U.S. Pat. No. 6,767,294 discloses a golf ball
comprising: i) a pressurized foamed inner center formed from a
thermoset material, a thermoplastic material, or combinations
thereof, a blowing agent and a cross-linking agent and, ii) an
outer core layer formed from a second thermoset material, a
thermoplastic material, or combinations thereof. Additionally, a
barrier resin or film can be applied over the outer core layer to
reduce the diffusion of the internal gas and pressure from the
nucleus (center and outer core layer). Preferred polymers for the
barrier layer have low permeability such as Saran.RTM. film (poly
(vinylidene chloride), Barex.RTM. resin (acyrlonitrile-co-methyl
acrylate), poly (vinyl alcohol), and PET film (polyethylene
terephthalate). The '294 Patent does not disclose core layers
having different hardness gradients.
[0016] Sullivan, Ladd, and Hebert, U.S. Pat. No. 7,708,654
discloses a golf ball having a foamed intermediate layer. Referring
to FIG. 1 in the '654 Patent, the golf ball includes a core (12),
an intermediate layer (14) made of a highly neutralized polymer
having a reduced specific gravity (less than 0.95), and a cover
(16). According to the '654 Patent, the intermediate layer can be
an outer core, a mantle layer, or an inner cover. The reduction in
specific gravity of the intermediate layer is caused by foaming the
composition of the layer and this reduction can be as high as 30%.
The '654 Patent discloses that other foamed compositions such as
foamed polyurethanes and polyureas may be used to form the
intermediate layer.
[0017] Tutmark, U.S. Pat. No. 8,272, 971 is directed to golf balls
containing an element that reduces the distance of the ball's
flight path. In one embodiment, the ball includes a core and cover.
A cavity is formed between core and cover and this may be filled by
a foamed polyurethane "middle layer" in order to dampen the ball's
flight properties. The foam of the middle layer is relatively light
in weight; and the core is relatively heavy and dense. According to
the '971 Patent, when a golfer strikes the ball with a club, the
foam in the middle layer actuates and compresses, thereby absorbing
much of the impact from the impact of the ball.
[0018] Although some foam core constructions for golf balls have
been considered over the years, there are drawbacks with using some
foam materials. For example, one drawback is that the foam center
(inner core) can be exposed to high temperatures during the
manufacturing process. These conditions can cause melting of the
foam centers and various other problems including, for example,
skinning of the center surface, partial or total collapse of the
foam, increased density, and center size reduction. Another
drawback is that some polyurethane foams can lose their elasticity
as the temperature changes. Other properties of these foam
compositions also may degrade when exposed to colder temperatures.
Golf ball cores are exposed to a wide range of high and low
temperatures during their life span. If the chemical and physical
properties of the foam composition change, the properties of the
resulting golf ball core may be adversely affected. For example,
there may be a negative impact on the size, resiliency, and
hardness of the foam core.
[0019] In view of some of the disadvantages with some foam
compositions, it would be desirable to have new foam compositions
and manufacturing methods for making foam core constructions. The
foam compositions should have good stability. The resulting foam
cores also should have good resiliency (rebounding performance),
thermal stability, and durability over a wide temperature range.
The manufacturing methods should effectively produce
uniformly-sized cores that are durable and will not deteriorate.
The present invention provides new foam core compositions, core
constructions, and manufacturing methods having such advantageous
features and other benefits. The invention also encompasses golf
balls containing the improved core assemblies.
SUMMARY OF THE INVENTION
[0020] The present invention provides a golf ball comprising a core
assembly and cover. The golf ball comprises an inner core layer
comprising a secondary heat-activated foam composition. The inner
core layer has a diameter in the range of about 0.100 to about
1.100 inches, preferably about 0.100 to about 0.900 inches; and a
specific gravity (SG.sub.inner) and a center hardness (H.sub.inner
core center), and ii) an outer core layer comprising a non-foamed
thermoset rubber composition, wherein the outer core layer is
disposed about the inner core and has a thickness in the range of
about 0.100 to about 0.750 inches, preferably about 0.250 to about
0.750 inches, and a specific gravity (SG.sub.outer) an outer
surface hardness (H.sub.outer surface of OC). Preferably, the
SG.sub.outer is greater than the SG.sub.inner,
[0021] In one version, the (H.sub.inner core center) is preferably
in the range of about 10 to about 60 Shore C and the (H.sub.outer
surface of OC) is preferably in the range of about 65 to about 96
Shore C to provide a positive hardness gradient across the core
assembly. In another version, the H.sub.inner core center is in the
range of about 10 to about 60 Shore C and the H.sub.outer surface
of OC is in the range of about 45 to about 96 Shore C.
[0022] The secondary heat-activated foam composition preferably
comprises primary and secondary chemical blowing agents. Water may
be used as the primary blowing agent. Suitable secondary blowing
agents include, for example, azo, nitroso, hydrazine, carbazide,
and hydrogen carbonate compounds, and mixtures thereof. Preferably,
the secondary blowing agent is
4,4'-oxybis(benzenesulfonylhydrazide) or sodium hydrogen
carbonate.
[0023] The method of this invention involves charging the polymer
materials, blowing agent, and any optional ingredients (for
example, fillers) to the mold. The composition is treated with
sufficient heat and pressure and the primary blowing agents are
activated, causing the polymer mixture to foam. The secondary
blowing agents are activated in a second molding step when the
outer core layer is molded over the inner core. In one embodiment,
the composition may further comprise expandable gas-containing
microspheres.
[0024] Thermoset or thermoplastic materials are used to form the
foamed inner core, and preferably a foamed polyurethane inner core
is formed. The foamed polyurethane may be prepared by adding water
in a sufficient amount to cause the mixture to foam, and a
secondary chemical blowing agent to a mixture of polyisocyanates,
polyols, curing agents, surfactants, and catalysts. Non-foamed
thermoset or thermoplastic materials also may be used to form the
outer core layer. Preferably, a thermoset rubber material such as
polybutadiene rubber is used. Thus, in one embodiment, the
dual-core includes a foam inner core (center) and a surrounding
non-foamed thermoset core layer that is preferably made from
polybutadiene rubber. In another embodiment, the dual-core includes
a foam inner core (center) and a surrounding non-foamed
thermoplastic core layer. For example, partially or highly
neutralized olefin acid copolymers or non-ionomeric polymers may be
used.
[0025] The core layers may have different specific gravity levels.
For example, the inner core layer may have a diameter in the range
of about 0.100 to about 0.900 inches, or 0.400 to 0.800 inches, and
a specific gravity in the range of about 0.25 to about 1.25 g/cc or
0.30 to 0.95 g/cc. In one version, the outer core layer has a
thickness in the range of about 0.250 to about 0.750 inches and a
specific gravity in the range of about 0.60 to about 2.90 g/cc.
[0026] The core layers also may have different hardness gradients.
For example, each core layer may have a positive, zero, or negative
hardness gradient. In a first embodiment, the inner core has a
positive hardness gradient; and the outer core layer has a positive
hardness gradient. In a second embodiment, the inner core has a
zero or negative hardness gradient; and the outer core layer has a
positive hardness gradient. In yet another embodiment, the inner
core has a positive hardness gradient, and the outer core layer has
zero or negative hardness gradient. In still another version, both
the inner and outer core layers have zero or negative hardness
gradients.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The novel features that are characteristic of the present
invention are set forth in the appended claims. However, the
preferred embodiments of the invention, together with further
objects and attendant advantages, are best understood by reference
to the following detailed description in connection with the
accompanying drawings in which:
[0028] FIG. 1 is a perspective view of a spherical inner core made
of a foamed composition in accordance with the present
invention;
[0029] FIG. 2 is a perspective view of one embodiment of upper and
lower mold cavities used to make the inner core of the present
invention;
[0030] FIG. 3 is a perspective view of a spherical inner core made
of a foamed composition and two half-shells made of a thermoset
rubber composition in accordance with the present invention;
[0031] FIG. 3A is a perspective view of one embodiment of upper and
lower mold cavities used to mold the outer core layer so that it
encapsulates the inner core of FIG. 3 in accordance with the
present invention;
[0032] FIG. 4 is a cross-sectional view of a four-piece golf ball
having a dual-layered core made in accordance with the present
invention;
[0033] FIG. 5 is a cross-sectional view of a three-piece golf ball
having a dual-layered core made in accordance with the present
invention; and
[0034] FIG. 6 is a perspective view of a finished golf ball having
a dimpled cover made in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Golf Ball Constructions
[0036] Golf balls having various constructions may be made in
accordance with this invention. For example, golf balls having
three piece, four-piece, and five-piece constructions with single
or multi-layered cover materials may be made. Representative
illustrations of such golf ball constructions are provided and
discussed further below. The term, "layer" as used herein means
generally any spherical portion of the golf ball. More
particularly, in one version, a three-piece golf ball containing a
dual-layered core and single-layered cover is made. The dual-core
includes an inner core (center) and surrounding outer core layer.
In another version, a four-piece golf ball containing a dual-core
and dual-cover (inner cover and outer cover layers) is made. In yet
another construction, a four-piece or five-piece golf ball
containing a dual-core; casing layer(s); and cover layer(s) may be
made. As used herein, the term, "casing layer" means a layer of the
ball disposed between the multi-layered core sub-assembly and
cover. The casing layer also may be referred to as a mantle or
intermediate layer. The diameter and thickness of the different
layers along with properties such as hardness and compression may
vary depending upon the construction and desired playing
performance properties of the golf ball.
[0037] Inner Core Composition
[0038] Preferably, the golf balls of this invention contain a core
structure comprising an inner core (center) and surrounding outer
core layer. In the present invention, "secondary heat-activated
foam compositions," are used to prepare the inner core (center)
structure of this invention. By the term, "secondary heat-activated
foam compositions," as used herein, it is meant foam materials
containing secondary chemical blowing agents that are activated
during over-molding of the foam center with a thermoset rubber
outer core layer composition.
[0039] In general, foam compositions are made by forming gas
bubbles in a polymer mixture using a foaming (blowing) agent. As
the bubbles form, the mixture expands and forms a foam composition
having either an open or closed cellular structure. Flexible foams
generally have an open cell structure, where the cells walls are
incomplete and contain small holes through which liquid and air can
permeate. Rigid foams generally have a closed cell structure, where
the cell walls are continuous and complete. Many foams contain both
open and closed cells. It also is possible to formulate flexible
foams having a closed cell structure and likewise to formulate
rigid foams having an open cell structure. Various thermoplastic
and thermoset materials may be used in forming the foam
compositions of this invention as discussed further below. In one
preferred embodiment, a polyurethane foam composition is
prepared.
[0040] The foaming (blowing) agents used to form the foam are
typically are in the form of powder, pellets, or liquids and they
are added to the composition, where they decompose or react during
heating and generate gaseous by-products (for example, nitrogen or
carbon dioxide). The gas is dispersed and trapped throughout the
composition and foams it. For example, water may be used as the
foaming agent. Air bubbles are introduced into the mixture of the
isocyanate and polyol compounds and water by high-speed mixing
equipment. As discussed in more detail further below, the
isocyanates react with the water to generate carbon dioxide which
fills and expands the cells created during the mixing process.
[0041] The chemical foaming agents may be inorganic, such as
ammonium carbonate and carbonates of alkalai metals, or may be
organic, such as azo and diazo compounds, such as nitrogen-based
azo compounds. Suitable azo compounds include, but are not limited
to, 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile),
and azodicarbonamide. Other compounds include, for example,
p,p'-oxybis(benzene sulfonyl hydrazide), p-toluene sulfonyl
semicarbazide, and p-toluene sulfonyl hydrazide. Other foaming
agents include any of the Celogens.RTM. sold by Crompton Chemical
Corporation, and nitroso compounds, sulfonylhydrazides, azides of
organic acids and their analogs, triazines, tri- and tetrazole
derivatives, sulfonyl semicarbazides, urea derivatives, guanidine
derivatives, and esters such as alkoxyboroxines. Also, foaming
agents that liberate gasses as a result of chemical interaction
between components such as mixtures of acids and metals, mixtures
of organic acids and inorganic carbonates, mixtures of nitriles and
ammonium salts, and the hydrolytic decomposition of urea may be
used. In the present invention, the foam composition preferably is
formed from primary and secondary chemical blowing agents.
[0042] Primary Chemical Blowing Agents--One or more primary
chemical blowing agents are added to the formulation that will be
foamed. Water is a preferred blowing agent. When added to the
polyurethane formulation, water will react with the isocyanate
groups and form carbamic acid intermediates. The carbamic acids
readily decarboxylate to form an amine and carbon dioxide. The
newly formed amine can then further react with other isocyanate
groups to form urea linkages and the carbon dioxide forms the
bubbles to produce the foam. The water is added in a sufficient
amount to cause the mixture to foam. In one preferred embodiment,
the water is present in the composition in an amount in the range
of 0.25 to 3.0% by weight based on total weight of the
composition.
[0043] Physical Blowing Agents--The physical blowing agents are
different materials and have different working mechanisms than the
chemical blowing agents. The physical blowing agents may be used,
in addition to or as an alternative to, the primary chemical
blowing agents. These blowing agents typically are gasses that are
introduced under high pressure directly into the polymer
composition. Chlorofluorocarbons (CFCs) and partially halogenated
chlorofluorocarbons are effective, but these compounds are banned
in many countries because of their environmental side effects.
Alternatively, aliphatic and cyclic hydrocarbon gasses such as
isobutene and pentane may be used. Inert gasses, such as carbon
dioxide and nitrogen, also are suitable. With physical blowing
agents, the isocyanate and polyol compounds react to form
polyurethane linkages and the reaction generates heat. Foam cells
are generated and as the foaming agent vaporizes, the gas becomes
trapped in the cells of the foam.
[0044] Secondary Chemical Blowing Agents--In the present invention,
one or more secondary chemical blowing agents are preferably added
to the formulation that will be foamed. Thus, in one preferred
version, the formulation contains a blend of primary and secondary
blowing agents. As discussed above, the blend of primary and
secondary blowing agents also may contain one or more physical
blowing agents. In another embodiment, the formulation contains a
blend of physical blowing agents and secondary blowing agents. The
secondary blowing agents are not activated during initial molding
of the foam center. Instead, these secondary blowing agents are
activated during the molding of the outer core layer onto the inner
core. In one preferred embodiment, the secondary blowing agent is
present in the composition in an amount in the range of 0.1 to 5.0%
by weight based on total weight of the composition, and more
preferably in the range of 0.5 to 3.0%.
[0045] The secondary blowing agents may be selected, for example,
from the group consisting of azo compounds such as azodicarbonamide
(ADCA) and azobisformamide; nitroso compounds such as
N,N-dimethyl-N,N-dinitroso terephthalamide,
N,N-dinitroso-pentamethylene-tetramine (DPT), and 5-Phenyltetrazole
(5 PT); hydrazine derivatives such as
4,4'-Oxybis(benzenesulfonylhydrazide) (OBSH), hydrazodicarbonamide
(HDCA), toluenesulfonyl hydrazide (TSH), and
benzene-sulfonyl-hydrazide (BSH), carbazide compounds such as
toluenesulfonyl-semicarbazide (TSH); and hydrogen carbonates such
as sodium hydrogen carbonate (NaHCO.sub.3); and mixtures thereof.
Thus, the formulation may contain a mixture of secondary blowing
agents.
[0046] In one preferred embodiment, chemical blowing agents having
relatively low decomposition temperatures that complement the
heating temperatures in the molding cycle are used. These blowing
agents will start to decompose as the designated temperature in the
molding process, and the foaming reaction will proceed more
quickly. For example, the secondary blowing may be selected from
the group consisting of OBSH, having a decomposition temperature of
about 160.degree. C. and NaHCO.sub.3 having a decomposition
temperature of about 150.degree. C. These blowing agents are
commercially available from such companies as Tramaco, GmbH
(Pinneberg, Germany) and Eiwa Chemical Ind. Co., Ltd. (Mitsubishi
Gas Chemical America, Inc., Detroit, Mich.).
[0047] It is recognized that during the decomposition reaction of
certain chemical foaming agents, more heat and energy is released
than is needed for the reaction. Once the decomposition has
started, it continues for a relatively long time period. If these
foaming agents are used, longer cooling periods are generally
required. Hydrazide and azo-based compounds often are used as
exothermic foaming agents. On the other hand, endothermic foaming
agents need energy for decomposition. Thus, the release of the
gasses quickly stops after the supply of heat to the composition
has been terminated. If the composition is produced using these
foaming agents, shorter cooling periods are needed. Bicarbonate and
citric acid-based foaming agents can be used as exothermic foaming
agents.
[0048] Additional Blowing Agents--Other suitable blowing agents
that may be added to the formulation that will be foamed in
accordance with this invention include, for example, expandable
gas-containing microspheres. Exemplary microspheres consist of an
acrylonitrile polymer shell encapsulating a volatile gas, such as
isopentane gas. This gas is contained within the sphere as a
blowing agent. In their unexpanded state, the diameter of these
hollow spheres range from 10 to 17 .mu.m and have a true density of
1000 to 1300 kg/m.sup.3. When heated, the gas inside the shell
increases its pressure and the thermoplastic shell softens,
resulting in a dramatic increase of the volume of the microspheres.
Fully expanded, the volume of the microspheres will increase more
than 40 times (typical diameter values would be an increase from 10
to 40 .mu.m), resulting in a true density below 30 kg/m.sup.3 (0.25
lbs/gallon). Typical expansion temperatures range from
80-190.degree. C. (176-374.degree. F.). Such expandable
microspheres are commercially available as Expancel.RTM. from
Expancel of Sweden or Akzo Nobel.
[0049] In the process of this invention, the materials used to
prepare the foam are charged to the mold for producing the inner
core. The mold may be equipped with steam nozzles so that steam can
be injected into the mold cavity. The temperature inside of the
mold can vary, for example, the temperature can range from about
80.degree. C. to about 400.degree. C. Steam, hot air, hot water, or
radiant heat may be used to foam the composition. The composition
expands as it is heated. The temperature must be chosen carefully
and must be sufficiently high so that it activates the primary
blowing agents and foams the mixture, but it must not be
excessively high so that it activates the secondary blowing agents.
In general, the temperature should be in the range of about room
temperature (RT) to about 180.degree. F. and preferably in the
range of about room temperature (RT) to about 150.degree. F. so
that it activates the primary blowing agents. Once the polymer
materials, blowing agent, and any optional ingredients (for
example, fillers) are charged to the mold and treated with
sufficient heat and pressure, the primary blowing agents are
activated. This causes the polymer mixture to foam and form the
primary heat-activated foam composition in the mold. The primary
heat-activated foam composition further contains secondary blowing
agents that are not activated during this initial molding step.
Rather, these secondary blowing agents are activated in a second
molding step when the outer core layer is molded over the inner
core as discussed further below.
[0050] Foam Polymers. As discussed above, polyurethane foam is
preferably prepared in accordance with this invention. It is
recognized, however, that a wide variety of thermoplastic and
thermoset materials may be used in forming the foam compositions of
this invention including, for example, polyurethanes; polyureas;
copolymers, blends and hybrids of polyurethane and polyurea;
olefin-based copolymer ionomer resins (for example, Surlyn.RTM.
ionomer resins and DuPont HPF.RTM. 1000 and HPF.RTM. 2000,
commercially available from DuPont; Iotek.RTM. ionomers,
commercially available from ExxonMobil Chemical Company;
Amplify.RTM. IO ionomers of ethylene acrylic acid copolymers,
commercially available from Dow Chemical Company; and Clarix.RTM.
ionomer resins, commercially available from A. Schulman Inc.);
polyethylene, including, for example, low density polyethylene,
linear low density polyethylene, and high density polyethylene;
polypropylene; rubber-toughened olefin polymers; acid copolymers,
for example, poly(meth)acrylic acid, which do not become part of an
ionomeric copolymer; plastomers; flexomers;
styrene/butadiene/styrene block copolymers;
styrene/ethylene-butylene/styrene block copolymers; dynamically
vulcanized elastomers; copolymers of ethylene and vinyl acetates;
copolymers of ethylene and methyl acrylates; polyvinyl chloride
resins; polyamides, poly(amide-ester) elastomers, and graft
copolymers of ionomer and polyamide including, for example,
Pebax.RTM. thermoplastic polyether block amides, commercially
available from Arkema Inc; cross-linked trans-polyisoprene and
blends thereof; polyester-based thermoplastic elastomers, such as
Hytrel.RTM., commercially available from DuPont or RiteFlex.RTM.,
commercially available from Ticona Engineering Polymers;
polyurethane-based thermoplastic elastomers, such as
Elastollan.RTM., commercially available from BASF; synthetic or
natural vulcanized rubber; and combinations thereof.
[0051] Castable polyurethanes, polyureas, and hybrids of
polyurethanes-polyureas are particularly desirable because these
materials can be used to make a golf ball having good playing
performance properties as discussed further below. By the term,
"hybrids of polyurethane and polyurea," it is meant to include
copolymers and blends thereof. Basically, polyurethane compositions
contain urethane linkages formed by the reaction of a
multi-functional isocyanate containing two or more NCO groups with
a polyol having two or more hydroxyl groups (OH--OH) sometimes in
the presence of a catalyst and other additives. Generally,
polyurethanes can be produced in a single-step reaction (one-shot)
or in a two-step reaction via a prepolymer or quasi-prepolymer. In
the one-shot method, all of the components are combined at once,
that is, all of the raw ingredients are added to a reaction vessel,
and the reaction is allowed to take place. In the prepolymer
method, an excess of polyisocyanate is first reacted with some
amount of a polyol to form the prepolymer which contains reactive
NCO groups. This prepolymer is then reacted again with a chain
extender or curing agent polyol to form the final polyurethane.
Polyurea compositions, which are distinct from the above-described
polyurethanes, also can be formed. In general, polyurea
compositions contain urea linkages formed by reacting an isocyanate
group (--N.dbd.C.dbd.O) with an amine group (NH or NH.sub.2).
Polyureas can be produced in similar fashion to polyurethanes by
either a one shot or prepolymer method. In forming a polyurea
polymer, the polyol would be substituted with a suitable polyamine.
Hybrid compositions containing urethane and urea linkages also may
be produced. For example, when polyurethane prepolymer is reacted
with amine-terminated curing agents during the chain-extending
step, any excess isocyanate groups in the prepolymer will react
with the amine groups in the curing agent. The resulting
polyurethane-urea composition contains urethane and urea linkages
and may be referred to as a hybrid. In another example, a hybrid
composition may be produced when a polyurea prepolymer is reacted
with a hydroxyl-terminated curing agent. A wide variety of
isocyanates, polyols, polyamines, and curing agents can be used to
form the polyurethane and polyurea compositions as discussed
further below.
[0052] More particularly, the foam inner core of this invention may
be prepared from a composition comprising an aromatic polyurethane,
which is preferably formed by reacting an aromatic diisocyanate
with a polyol. Suitable aromatic diisocyanates that may be used in
accordance with this invention include, for example, toluene
2,4-diisocyanate (TDI), toluene 2,6-diisocyanate (TDI),
4,4'-methylene diphenyl diisocyanate (MDI), 2,4'-methylene diphenyl
diisocyanate (MDI), polymeric methylene diphenyl diisocyanate
(PMDI), p-phenylene diisocyanate (PPDI), m-phenylene diisocyanate
(PDI), naphthalene 1,5-diisocyanate (NDI), naphthalene
2,4-diisocyanate (NDI), p-xylene diisocyanate (XDI), and
homopolymers and copolymers and blends thereof. The aromatic
isocyanates are able to react with the hydroxyl or amine compounds
and form a durable and tough polymer having a high melting point.
The resulting polyurethane generally has good mechanical strength
and tear-resistance.
[0053] Alternatively, the foamed composition of the inner core may
be prepared from a composition comprising aliphatic polyurethane,
which is preferably formed by reacting an aliphatic diisocyanate
with a polyol. Suitable aliphatic diisocyanates that may be used in
accordance with this invention include, for example, isophorone
diisocyanate (IPDI), 1,6-hexamethylene diisocyanate (HDI),
4,4'-dicyclohexylmethane diisocyanate ("H.sub.12 MDI"),
meta-tetramethylxylyene diisocyanate (TMXDI), trans-cyclohexane
diisocyanate (CHDI), 1,3-bis(isocyanatomethyl)cyclohexane;
1,4-bis(isocyanatomethyl)cyclohexane; and homopolymers and
copolymers and blends thereof. The resulting polyurethane generally
has good light and thermal stability. Preferred polyfunctional
isocyanates include 4,4'-methylene diphenyl diisocyanate (MDI),
2,4'-methylene diphenyl diisocyanate (MDI), and polymeric MDI
having a functionality in the range of 2.0 to 3.5 and more
preferably 2.2 to 2.5.
[0054] Any suitable polyol may be used to react with the
polyisocyanate in accordance with this invention. Exemplary polyols
include, but are not limited to, polyether polyols,
hydroxy-terminated polybutadiene (including partially/fully
hydrogenated derivatives), polyester polyols, polycaprolactone
polyols, and polycarbonate polyols. In one preferred embodiment,
the polyol includes polyether polyol. Examples include, but are not
limited to, polytetramethylene ether glycol (PTMEG), polyethylene
propylene glycol, polyoxypropylene glycol, and mixtures thereof.
The hydrocarbon chain can have saturated or unsaturated bonds and
substituted or unsubstituted aromatic and cyclic groups.
Preferably, the polyol of the present invention includes PTMEG.
[0055] As discussed further below, chain extenders (curing agents)
are added to the mixture to build-up the molecular weight of the
polyurethane polymer. In general, hydroxyl-terminated curing
agents, amine-terminated curing agents, and mixtures thereof are
used.
[0056] A catalyst may be employed to promote the reaction between
the isocyanate and polyol compounds. Suitable catalysts include,
but are not limited to, bismuth catalyst; zinc octoate; tin
catalysts such as bis-butyltin dilaurate, bis-butyltin diacetate,
stannous octoate; tin (II) chloride, tin (IV) chloride,
bis-butyltin dimethoxide, dimethyl-bis[1-oxonedecyl)oxy]stannane,
di-n-octyltin bis-isooctyl mercaptoacetate; amine catalysts such as
triethylenediamine, triethylamine, tributylamine,
1,4-diaza(2,2,2)bicyclooctane, tetramethylbutane diamine,
bis[2-dimethylaminoethyl]ether, N,N-dimethylaminopropylamine,
N,N-dimethylcyclohexylamine,
N,N,N',N',N''-pentamethyldiethylenetriamine, diethanolamine,
dimethtlethanolamine,
N-[2-(dimethylamino)ethyl]-N-methylethanolamine, N-ethylmorpholine,
3-dimethylamino-N,N-dimethylpropionamide, and
N,N',N''-dimethylaminopropylhexahydrotriazine; organic acids such
as oleic acid and acetic acid; delayed catalysts; and mixtures
thereof. Zirconium-based catalysts such as, for example,
bis(2-dimethyl aminoethyl) ether; mixtures of zinc complexes and
amine compounds such as KKAT.TM. XK 614, available from King
Industries; and amine catalysts such as Niax.TM. A-2 and A-33,
available from Momentive Specialty Chemicals, Inc. are particularly
preferred. The catalyst is preferably added in an amount sufficient
to catalyze the reaction of the components in the reactive mixture.
In one embodiment, the catalyst is present in an amount from about
0.001 percent to about 1 percent, and preferably 0.1 to 0.5
percent, by weight of the composition.
[0057] In one preferred embodiment, as described above, water is
used as the foaming agent--the water reacts with the polyisocyanate
compound(s) and forms carbon dioxide gas which induces foaming of
the mixture. The reaction rate of the water and polyisocyanate
compounds affects how quickly the foam is formed as measured per
reaction profile properties such as cream time, gel time, and rise
time of the foam.
[0058] The hydroxyl chain-extending (curing) agents are preferably
selected from the group consisting of ethylene glycol; diethylene
glycol; polyethylene glycol; propylene glycol;
2-methyl-1,3-propanediol; 2-methyl-1,4-butanediol;
monoethanolamine; diethanolamine; triethanolamine;
monoisopropanolamine; diisopropanolamine; dipropylene glycol;
polypropylene glycol; 1,2-butanediol; 1,3-butanediol;
1,4-butanediol; 2,3-butanediol; 2,3-dimethyl-2,3-butanediol;
trimethylolpropane; cyclohexyldimethylol; triisopropanolamine;
N,N,N',N'-tetra-(2-hydroxypropyl)-ethylene diamine; diethylene
glycol bis-(aminopropyl) ether; 1,5-pentanediol; 1,6-hexanediol;
1,3-bis-(2-hydroxyethoxy) cyclohexane; 1,4-cyclohexyldimethylol;
1,3-bis-[2-(2-hydroxyethoxy) ethoxy] cyclohexane;
1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}cyclohexane;
trimethylolpropane; polytetramethylene ether glycol (PTMEG),
preferably having a molecular weight from about 250 to about 3900;
and mixtures thereof. Di, tri, and tetra-functional
polycaprolactone diols such as, 2-oxepanone polymer initiated with
1,4-butanediol, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, or
2,2-bis(hydroxymethyl)-1,3-propanediol such, may be used.
[0059] Suitable amine chain-extending (curing) agents that can be
used in chain-extending the polyurethane prepolymer include, but
are not limited to, unsaturated diamines such as
4,4'-diamino-diphenylmethane (i.e., 4,4'-methylene-dianiline or
"MDA"), m-phenylenediamine, p-phenylenediamine, 1,2- or
1,4-bis(sec-butylamino)benzene, 3,5-diethyl-(2,4- or
2,6-)toluenediamine or "DETDA", 3,5-dimethylthio-(2,4- or
2,6-)toluenediamine, 3,5-diethylthio-(2,4- or 2,6-)toluenediamine,
3,3'-dimethyl-4,4'-diamino-diphenylmethane,
3,3'-diethyl-5,5'-dimethyl4,4'-diamino-diphenylmethane (i.e.,
4,4'-methylene-bis(2-ethyl-6-methyl-benezeneamine)),
3,3'-dichloro-4,4'-diamino-diphenylmethane (i.e.,
4,4'-methylene-bis(2-chloroaniline) or "MOCA"),
3,3',5,5'-tetraethyl-4,4'-diamino-diphenylmethane (i.e.,
4,4'-methylene-bis(2,6-diethylaniline),
2,2'-dichloro-3,3',5,5'-tetraethyl-4,4'-diamino-diphenylmethane
(i.e., 4,4'-methylene-bis(3-chloro-2,6-diethyleneaniline) or
"MCDEA"), 3,3'-diethyl-5,5'-dichloro-4,4'-diamino-diphenylmethane,
or "MDEA"),
3,3'-dichloro-2,2',6,6'-tetraethyl-4,4'-diamino-diphenylmethane,
3,3'-dichloro-4,4'-diamino-diphenylmethane,
4,4'-methylene-bis(2,3-dichloroaniline) (i.e.,
2,2',3,3'-tetrachloro-4,4'-diamino-diphenylmethane or "MDCA"),
4,4'-bis(sec-butylamino)-diphenylmethane,
N,N'-dialkylamino-diphenylmethane,
trimethyleneglycol-di(p-aminobenzoate),
polyethyleneglycol-di(p-aminobenzoate),
polytetramethyleneglycol-di(p-aminobenzoate); saturated diamines
such as ethylene diamine, 1,3-propylene diamine,
2-methyl-pentamethylene diamine, hexamethylene diamine, 2,2,4- and
2,4,4-trimethyl-1,6-hexane diamine, imino-bis(propylamine),
imido-bis(propylamine), methylimino-bis(propylamine) (i.e.,
N-(3-aminopropyl)-N-methyl-1,3-propanediamine),
1,4-bis(3-aminopropoxy)butane (i.e.,
3,3'-[1,4-butanediylbis-(oxy)bis]-1-propanamine),
diethyleneglycol-bis(propylamine) (i.e.,
diethyleneglycol-di(aminopropyl)ether),
4,7,10-trioxatridecane-1,13-diamine,
1-methyl-2,6-diamino-cyclohexane, 1,4-diamino-cyclohexane,
poly(oxyethylene-oxypropylene) diamines, 1,3- or
1,4-bis(methylamino)-cyclohexane, isophorone diamine, 1,2- or
1,4-bis(sec-butylamino)-cyclohexane, N,N'-diisopropyl-isophorone
diamine, 4,4'-diamino-dicyclohexylmethane,
3,3'-dimethyl-4,4'-diamino-dicyclohexylmethane,
3,3'-dichloro-4,4'-diamino-dicyclohexylmethane,
N,N'-dialkylamino-dicyclohexylmethane, polyoxyethylene diamines,
3,3'-diethyl-5,5'-dimethyl-4,4'-diamino-dicyclohexylmethane,
polyoxypropylene diamines,
3,3'-diethyl-5,5'-dichloro-4,4'-diamino-dicyclohexylmethane,
polytetramethylene ether diamines,
3,3',5,5'-tetraethyl-4,4'-diamino-dicyclohexylmethane (i.e.,
4,4'-methylene-bis(2,6-diethylaminocyclohexane)),
3,3'-dichloro-4,4'-diamino-dicyclohexylmethane,
2,2'-dichloro-3,3',5,5'-tetraethyl-4,4'-diamino-dicyclohexylmethane,
(ethylene oxide)-capped polyoxypropylene ether diamines,
2,2',3,3'-tetrachloro-4,4'-diamino-dicyclohexylmethane,
4,4'-bis(sec-butylamino)-dicyclohexylmethane; triamines such as
diethylene triamine, dipropylene triamine, (propylene oxide)-based
triamines (i.e., polyoxypropylene triamines),
N-(2-aminoethyl)-1,3-propylenediamine (i.e., N.sub.3-amine),
glycerin-based triamines, (all saturated); tetramines such as
N,N'-bis(3-aminopropyl)ethylene diamine (i.e., N.sub.4-amine) (both
saturated), triethylene tetramine; and other polyamines such as
tetraethylene pentamine (also saturated). One suitable
amine-terminated chain-extending agent is Ethacure 300.TM.
(dimethylthiotoluenediamine or a mixture of
2,6-diamino-3,5-dimethylthiotoluene and
2,4-diamino-3,5-dimethylthiotoluene.) The amine curing agents used
as chain extenders normally have a cyclic structure and a low
molecular weight (250 or less).
[0060] When a hydroxyl-terminated curing agent is used, the
resulting polyurethane composition contains urethane linkages. On
the other hand, when an amine-terminated curing agent is used, any
excess isocyanate groups will react with the amine groups in the
curing agent. The resulting polyurethane composition contains
urethane and urea linkages and may be referred to as a
polyurethane/urea hybrid.
[0061] In addition to the polymer and foaming agent, the foam
composition also may include other ingredients such as, for
example, fillers, cross-linking agents, chain extenders,
surfactants, dyes and pigments, coloring agents, fluorescent
agents, adsorbents, stabilizers, softening agents, impact
modifiers, antioxidants, antiozonants, and the like. The
formulations used to prepare the polyurethane foam compositions of
this invention preferably contain a polyol, polyisocyanate, water,
an amine or hydroxyl curing agent, surfactant, and a catalyst as
described further below.
[0062] Fillers. The foam composition may contain fillers such as,
for example, mineral filler particulate. Suitable mineral filler
particulates include compounds such as zinc oxide, limestone,
silica, mica, barytes, lithopone, zinc sulfide, talc, calcium
carbonate, magnesium carbonate, clays, powdered metals and alloys
such as bismuth, brass, bronze, cobalt, copper, iron, nickel,
tungsten, aluminum, tin, precipitated hydrated silica, fumed
silica, mica, calcium metasilicate, barium sulfate, zinc sulfide,
lithopone, silicates, silicon carbide, diatomaceous earth,
carbonates such as calcium or magnesium or barium carbonate,
sulfates such as calcium or magnesium or barium sulfate. Silicon
dioxides are particularly preferred because they are based on Si--O
bonds and these material are compatible with the Si--O--Si backbone
of the silicone foam. Adding fillers to the composition provides
many benefits including helping improve the stiffness and strength
of the composition. The mineral fillers tend to help decrease the
size of the foam cells and increase cell density. The mineral
fillers also tend to help improve the physical properties of the
foam such as hardness, compression set, and tensile strength.
[0063] More particularly, clay particulate fillers, such as
Garamite.RTM. mixed mineral thixotropes and Cloisite.RTM. and
Nanofil.RTM. nanoclays, commercially available from Southern Clay
Products, Inc., and Nanomax.RTM. and Nanomer.RTM. nanoclays,
commercially available from Nanocor, Inc may be used. Other
nano-scale materials such as nanotubes and nanoflakes also may be
used. Also, talc particulate (e.g., Luzenac HAR.RTM. high aspect
ratio talcs, commercially available from Luzenac America, Inc.),
glass (e.g., glass flake, milled glass, and microglass), and
combinations thereof may be used. Metal oxide fillers have good
heat-stability and include, for example, aluminum oxide, zinc
oxide, tin oxide, barium sulfate, zinc sulfate, calcium oxide,
calcium carbonate, zinc carbonate, barium carbonate, tungsten,
tungsten carbide, and lead silicate fillers. These metal oxides and
other metal fillers such as, for example, particulate; powders;
flakes; and fibers of copper, steel, brass, tungsten, titanium,
aluminum, magnesium, molybdenum, cobalt, nickel, iron, lead, tin,
zinc, barium, bismuth, bronze, silver, gold, and platinum, and
alloys and combinations thereof may be added to the silicone foam
composition.
[0064] Surfactants. The foam composition also may contain
surfactants to stabilize the foam and help control the foam cell
size and structure. In one preferred version, the foam composition
includes silicone surfactant. In general, the surfactant helps
regulate the foam cell size and stabilizes the cell walls to
prevent the cells from collapsing. As discussed above, the liquid
reactants tend to react rapidly to form the foam. The "liquid" foam
develops into a solid silicone foam in a relatively short period of
time. If a silicone or other surfactant is not added, the
gas-liquid interface between the liquid reactants and expanding gas
bubbles may not support the stress. As a result, the cell window
can crack or rupture and there can be cell wall drainage. In turn,
the foam can collapse on itself. Adding a surfactant helps create a
surface tension gradient along the gas-liquid interface and helps
reduce cell wall drainage. The surfactant has a relatively low
surface tension and thus can lower the surface tension of the foam.
It is believed the surfactant orients itself the foam cell walls
and lowers the surface tension to create the surface tension
gradient. Blowing efficiency and nucleation are supported by adding
the surfactant and thus more bubbles are created in the system. The
surfactant also helps create a greater number of smaller sized foam
cells and increases the closed cell content of the foam due the
surfactant's lower surface tension. Thus, the cell structure in the
foam is maintained as the as gas is prevented from diffusing out
through the cell walls. Along with the decrease in cell size, there
is a decrease in thermal conductivity. The resulting foam material
tends to have greater compression strength and modulus. This may be
due to the increase in closed cell content and smaller cell
size.
[0065] As discussed further below, in one preferred embodiment, the
specific gravity (density) of the foam inner core is less than the
specific gravity of the outer core. If an excess amount of mineral
filler or other additives are included in the foam composition,
they should not be added in an amount that would increase the
specific gravity (density) of the foam inner core to a level such
that it would be greater than the specific gravity of the outer
core layer. If the ball's mass is concentrated towards the outer
surface (for example, outer core layers), and the outer core layer
has a higher specific gravity than the inner core, the ball has a
relatively high Moment of Inertia (MOI). In such balls, most of the
mass is located away from the ball's axis of rotation and thus more
force is needed to generate spin. These balls have a generally low
spin rate as the ball leaves the club's face after contact between
the ball and club. Such core structures (wherein the specific
gravity of the outer core is greater than the specific gravity of
the inner core) are preferred in the present invention. Thus, in
one preferred embodiment, the concentration of mineral filler
particulate in the foam composition is in the range of about 0.1 to
about 9.0% by weight.
[0066] Outer Core Composition
[0067] As discussed above, the inner core (center) is made
preferably from a foamed polyurethane composition. Preferably, a
two-layered or dual-core is made, wherein the inner core is
surrounded by an outer core layer. In one preferred embodiment, the
outer core layer is formed from a non-foamed thermoset composition
and more preferably from a non-foamed thermoset rubber
composition.
[0068] Suitable thermoset rubber materials that may be used to form
the outer core layer include, but are not limited to,
polybutadiene, polyisoprene, ethylene propylene rubber ("EPR"),
ethylene-propylene-diene ("EPDM") rubber, styrene-butadiene rubber,
styrenic block copolymer rubbers (such as "SI", "SIS", "SB", "SBS",
"SIBS", and the like, where "S" is styrene, "I" is isobutylene, and
"B" is butadiene), polyalkenamers such as, for example,
polyoctenamer, butyl rubber, halobutyl rubber, polystyrene
elastomers, polyethylene elastomers, polyurethane elastomers,
polyurea elastomers, metallocene-catalyzed elastomers and
plastomers, copolymers of isobutylene and p-alkylstyrene,
halogenated copolymers of isobutylene and p-alkylstyrene,
copolymers of butadiene with acrylonitrile, polychloroprene, alkyl
acrylate rubber, chlorinated isoprene rubber, acrylonitrile
chlorinated isoprene rubber, and blends of two or more thereof.
Preferably, the outer core layer is formed from a polybutadiene
rubber composition.
[0069] In the present invention, the inner core (center) comprises
a foam thermoplastic or thermoset polymer composition that may be
prepared using the above-described methods. Preferably, the center
comprises a polyurethane foam composition. The foam may have an
open or closed cellular structure or combinations thereof and may
range from relatively rigid foam to very flexible foam. Referring
to FIG. 1, a foamed inner core (4) having a geometric center (6)
and outer skin (8) may be prepared in accordance with this
invention.
[0070] As discussed above, the inner core structure is prepared
from a secondary heat-activated foam composition. Referring to FIG.
2, one version of a mold for preparing the foamed inner core is
shown. The mold includes lower and upper mold cavities (9, 10) that
are placed in lower and upper mold frame plates (11, 12). The frame
plates (11, 12) contain guide pins and complementary alignment
holes (not shown in drawing). The guide pins are inserted into the
alignment holes to secure the lower plate (11) to the upper plate
(12). The lower and upper mold cavities (9, 10) are mated together
as the frame plates (11, 12) are fastened. When the lower and upper
mold cavities (9, 10) are joined together, they define an interior
spherical cavity that houses the spherical core. The upper mold
contains a vent or hole (14) to allow for the expanding foam to
fill the cavities uniformly. A secondary overflow chamber (16),
which is located above the vent (14), can be used to adjust the
amount of foam overflow and thus adjust the density of the core
structure being molded in the cavities. As the lower and upper mold
cavities (9, 10) are mated together and sufficient heat and
pressure is applied, the particles fuse together, cure and solidify
to form a relatively rigid or flexible and lightweight spherical
core. The resulting cores are cooled and then removed from the
mold.
[0071] Meanwhile, the outer core layer is prepared by an
over-molding process, wherein the outer core layer (preferably a
non-foamed thermoset rubber composition) is molded over the inner
core. The outer core layer may be molded over the foamed inner core
using a variety of molding techniques.
[0072] For example, the outer core composition (preferably a
thermoset rubber composition as described above) may be
injection-molded or compression-molded to produce half-shells.
These smooth-surfaced hemispherical shells are then placed around
the foamed, spherical inner core in a compression mold. Under
sufficient heating and pressure, the shells fuse together to form
an outer core layer that encapsulates the foamed inner core. More
particularly, as shown in FIGS. 3 and 3A, after the two half-shells
(17a 17b) made from a rubber or other composition have been
prepared, they are joined together in a mold to encase the
previously molded inner core (4). The hemispherical shells (17a,
17b) and inner core (4) are placed in a mold between a first mold
member (17a) and a second mold member (17b). The first and second
mold members (19, 19) are subsequently pressed together to join
together the half-shells (17a, 17b) under sufficient hat and
pressure. This molding process forms the outer core layer. As a
result, a finished core assembly (inner core and surrounding outer
core layer) is produced.
[0073] In another method, the outer core composition may be added
to an injection-molding machine. After the foamed inner core has
been positioned properly in the injection-molding cavity, the outer
core composition is injection-molded directly over the inner core.
In yet another method, the outer core layer may be formed by
compression-molding the outer core composition directly around the
inner core.
[0074] During the over-molding of the foamed center with the
thermoset rubber outer core layer composition, the heat used in the
curing stage of the molding cycle activates/decomposes the
secondary chemical blowing agent. This step releases a sufficient
quantity of gaseous by-product (for example CO.sub.2 or nitrogen)
to maintain and preserve the size, density and cell structure of
the foam core. As discussed above, the secondary blowing agents can
be endothermic or exothermic, and can be used solely or in various
combinations. Different secondary blowing agents are available with
many different decomposition temperatures. Selection of the
appropriate secondary blowing agent is determined by coordinating
the molding cycle temperature and time period from the start of the
cycle to the decomposition temperature of the blowing agent(s). In
addition other catalysts can be used to accelerate decomposition of
blowing agent. One drawback with conventional core constructions
having a foam center and surrounding thermoset rubber outer core
layer is that foam centers can undergo significant changes in
physical properties when subjected to temperatures and pressures
outside their design criteria. In some instances, the foam centers
can actually melt and soften. For example, in standard
manufacturing operations, during molding of the rubber outer-core
layers, mold temperatures in excess of 300.degree. F. are used for
heat cycles of 15 minutes or longer, along with significant
compressive forces. Additionally, the interior of the outer core
can see a substantial spike in temperature due to the chemical
exothermic reaction that occurs as the cross-linking peroxides
decompose. This can cause melting of the foam centers and lead to
various problems including skinning of the center surface, partial
or total collapse of the foam, increased density, and center size
reduction.
[0075] As discussed above, the present invention overcomes these
drawbacks by using secondary heat-activated foam compositions in
the manufacturing of the core structure. The foam materials contain
secondary chemical blowing agents that are activated during
over-molding of the foam center with a thermoset rubber outer core
layer composition. In the present invention, the foam composition
is preferably formed from primary and secondary chemical blowing
agents. One or more primary chemical blowing agents are added to
the inner core formulation that will be foamed. Water is a
preferred primary chemical blowing agent. When added to the
polyurethane formulation, water will react with the isocyanate
groups and form carbamic acid intermediates. The carbamic acids
readily decarboxylate to form an amine and carbon dioxide. The
newly formed amine can then further react with other isocyanate
groups to form urea linkages and the carbon dioxide forms the
bubbles to produce the foam. One or more secondary chemical blowing
agents also are added to the formulation that will be foamed. These
secondary blowing agents are not activated during initial molding
of the foam center. Instead, these secondary blowing agents are
activated during the molding of the outer core layer onto the inner
core.
[0076] The materials used to prepare the foam are charged to the
mold for producing the inner core. The mold may be equipped with
steam nozzles so that steam can be injected into the mold cavity.
The temperature inside of the mold can vary, for example, the
temperature can range from about 80.degree. C. to about 400.degree.
C. Steam, hot air, hot water, or radiant heat may be used to foam
the composition. The composition expands as it is heated. The
temperature must be chosen carefully and must be sufficiently high
so that it activates the primary blowing agents and foams the
mixture, but it must not be excessively high so that it activates
the secondary blowing agents. In general, the temperature should be
in the range of about 80.degree. C. to about 250.degree. C. and
preferably in the range of about 90.degree. C. to about 220.degree.
C. so that it activates the primary blowing agents. Once the
polymer materials, blowing agent, and any optional ingredients (for
example, fillers) are charged to the mold and treated with
sufficient heat and pressure, the primary blowing agents are
activated. This causes the polymer mixture to foam and form the
primary heat-activated foam composition in the mold. The primary
heat-activated foam composition further contains secondary blowing
agents that are not activated during this initial molding step.
Rather, these secondary blowing agents are activated in a second
molding step when the outer core layer is molded over the inner
core as discussed further below. This process helps maintain and
preserve the size, density and cell structure of the foam core.
[0077] Properties of Foams
[0078] The foam compositions of this invention have numerous
chemical and physical properties making them suitable for core
assemblies in golf balls.
[0079] The density of the foam is an important property and is
defines as the weight per unit volume (typically, g/cm.sup.3) and
can be measured per ASTM D-1622. The hardness, stiffness, and
load-bearing capacity of the foam are independent of the foam's
density, although foams having a high density typically have high
hardness and stiffness. Normally, foams having higher densities
have higher compression strength. Surprisingly, the foam
compositions used to produce the inner core of the golf balls per
this invention have a relatively low density; however, the foams
are not necessarily soft and flexible, rather, they may be
relatively firm, rigid, or semi-rigid depending upon the desired
golf ball properties. Tensile strength, tear-resistance, and
elongation generally refer to the foam's ability to resist breaking
or tearing, and these properties can be measured per ASTM D-1623.
The durability of foams is important, because introducing fillers
and other additives into the foam composition can increase the
tendency of the foam to break or tear apart. In general, the
tensile strength of the foam compositions of this invention is in
the range of about 20 to about 1000 psi (parallel to the foam rise)
and about 50 to about 1000 psi (perpendicular to the foam rise) as
measured per ASTM D-1623 at 23.degree. C. and 50% relative humidity
(RH). Meanwhile, the flex modulus of the foams of this invention is
generally in the range of about 5 to about 45 kPa as measured per
ASTM D-790, and the foams generally have a compressive modulus of
200 to 50,000 psi.
[0080] In another test, compression strength is measured on an
Instron machine according to ASTM D-1621. The foam is cut into
blocks and the compression strength is measured as the force
required to compress the block by 10%. In general, the compressive
strength of the foam compositions of this invention is in the range
of about 100 to about 1800 psi (parallel and perpendicular to the
foam rise) as measured per ASTM D-1621 at 23.degree. C. and 50%
relative humidity (RH). The test is conducted perpendicular to the
rise of the foam or parallel to the rise of the foam. The
Percentage (%) of Compression Set also can be used. This is a
measure of the permanent deformation of a foam sample after it has
been compressed between two metal plates under controlled time and
temperature condition (standard--22 hours at 70.degree. C.
(158.degree. F.)). The foam is compressed to a thickness given as a
percentage of its original thickness that remained "set."
Preferably, the Compression Set of the foam is less than ten
percent (10%), that is, the foam recovers to a point of 90% or
greater of its original thickness.
[0081] Hardness of the Inner Core
[0082] As shown in FIG. 1, a foamed inner core (4) having a
geometric center (6) and outer skin (8) may be prepared per the
molding method discussed above. The outer skin (8) is generally a
non-foamed region that forms the outer surface of the core
structure. As discussed above, in one method of this invention,
pre-formed polyurethane foam particles are formed and these
particles are coated with a heat-activatable binder. In another
method, the foam particles are not coated with a binder. These
uncoated particles are heat-treated and the particles are pressed
together. Because the outer skin (8) of the particles is normally a
non-foamed region, the adjacent particles can fuse together more
easily. The non-foamed outer skin (8) also helps the particles to
bond to each other when the particles are coated with a
heat-activated binder.
[0083] The resulting inner core preferably has a diameter within a
range of about 0.100 to about 1.100 inches. For example, the inner
core may have a diameter within a range of about 0.250 to about
1.000 inches. In another example, the inner core may have a
diameter within a range of about 0.300 to about 0.800 inches. More
particularly, the inner core preferably has a diameter size with a
lower limit of about 0.10 or 0.12 or 0.15 or 0.17 or 0.25 or 0.30
or 0.35 or 0.38 or 0.45 or 0.50 or 0.52 or 0.55 inches and an upper
limit of about 0.60 or 0.63 or 0.65 or 0.70 or 0.74 or 0.80 or 0.86
or 0.90 or 0.95 or 1.00 or 1.02 or 1.10 inches. The outer skin (8)
of the inner core is relatively thin preferably having a thickness
of less than about 0.020 inches and more preferably less than 0.010
inches. In one preferred embodiment, the foamed core has a
"positive" hardness gradient (that is, the outer skin of the inner
core is harder than its geometric center.)
[0084] For example, the geometric center hardness of the inner core
(H.sub.inner core center), as measured in Shore C units, may be
about 10 Shore C or greater and preferably has a lower limit of
about 10 or 13 or 16 or 20 or 25 or 30 or 32 or 34 or 36 or 40
Shore C and an upper limit of about 42 or 44 or 48 or 50 or 52 or
56 or 60 or 62 or 65 or 68 or 70 or 74 or 78 or 80 or 84 or 90
Shore C. In one preferred version, the geometric center hardness of
the inner core (H.sub.inner core center) is about 40 Shore C.
[0085] When a flexible, relatively soft foam is used, the
(H.sub.inner core center) of the foam may have a Shore A hardness
of about 10 or greater, and preferably has a lower limit of 15, 18,
20, 25, 28, 30, 35, 38, or 40 Shore A hardness and an upper limit
of about 45 or 48, or 50, 54, 58, 60, 65, 70, 80, 85, or 90 Shore A
hardness. In one preferred embodiment, the (H.sub.inner core
center) of the foam is about 55 Shore A.
[0086] The H.sub.inner core center, as measured in Shore D units,
is about 15 Shore D or greater and more preferably within a range
having a lower limit of about 15 or 18 or 20 or 22 or 25 or 28 or
30 or 32 or 36 or 40 or 44 Shore D and an upper limit of about 45
or 48 or 50 or 52 or 55 or 58 or 60 or 62 or 64 or 66 or 70 or 72
or 74 or 78 or 80 or 82 or 84 or 88 or 90 Shore D.
[0087] Meanwhile, the outer surface hardness of the inner core
(H.sub.inner core surface), as measured in Shore C, is preferably
about 20 Shore C or greater and may have, for example, a lower
limit of about 10 or 14 or 17 or 20 or 22 or 24 or 28 or 30 or 32
or 35 or 36 or 40 or 42 or 44 or 48 or 50 Shore C and an upper
limit of about 52 or 55 or 58 or 60 or 62 or 64 or 66 or 70 or 74
or 78 or 80 or 86 or 88 or 90 or 92 or 95 Shore C. When a flexible,
relatively soft foam is used, the (H.sub.inner core surface) of the
foam may have a Shore A hardness of about 12 or greater, and
preferably has a lower limit of 12, 16, 20, 24, 26, 28, 30, 34, 40,
42, 46, or 50 Shore A hardness and an upper limit of about 52, 55,
58, 60, 62, 66, 70, 74, 78, 80, 84, 88, 90, or 95 Shore A hardness.
In one preferred embodiment, the (H.sub.inner core surface) is
about 60 Shore A. The (H.sub.inner core surface), as measured in
Shore D units, preferably has a lower limit of about 25 or 28 or 30
or 32 or 36 or 40 or 44 Shore D and an upper limit of about 45 or
48 or 50 or 52 or 55 or 58 or 60 or 62 or 64 or 66 or 70 or 74 or
78 or 80 or 82 or 84 or 88 or 90 or 94 or 96 Shore D.
[0088] Density of the Inner Core
[0089] The foamed inner core preferably has a specific gravity of
about 0.20 to about 1.00 g/cc. That is, the density of the inner
core (as measured at any point of the inner core structure) is
preferably within the range of about 0.20 to about 1.00 g/cc. By
the term, "specific gravity of the inner core" ("SG.sub.inner"), it
is generally meant the specific gravity of the inner core as
measured at any point of the inner core structure. It should be
understood, however, that the specific gravity values, as taken at
different particular points of the inner core structure, may vary.
For example, the foamed inner core may have a "positive" density
gradient (that is, the outer surface (skin) of the inner core may
have a density greater than the geometric center of the inner
core.) In one preferred version, the specific gravity of the
geometric center of the inner core (SG.sub.center of inner core) is
less than 0.80 g/cc and more preferably less than 0.70 g/cc. More
particularly, in one version, the (SG.sub.center of inner core) is
in the range of about 0.10 to about 0.06 g/cc. For example, the
(SG.sub.center of inner core) may be within a range having a lower
limit of about 0.10 or 0.15 of 0.20 or 0.24 or 0.30 or 0.35 or 0.37
or 0.40 or 0.42 or 0.45 or 0.47 or 0.50 and an upper limit of about
0.60 or 0.65 or 0.70 or 0.74 or 0.78 or 0.80, or 0.82 or 0.84 or
0.85 or 0.88 or 0.90 g/cc. Meanwhile, the specific gravity of the
outer surface (skin) of the inner core (SG.sub.skin of inner core),
in one preferred version, is greater than about 0.90 g/cc and more
preferably greater than 1.00 g/cc. For example, the (SG.sub.skin of
inner core) may fall within the range of about 0.90 to about 1.25
g/cc. More particularly, in one version, the (SG.sub.skin of inner
core) may have a specific gravity with a lower limit of about 0.90
or 0.92 or 0.95 or 0.98 or 1.00 or 1.02 or 1.06 or 1.10 g/cc and an
upper limit of about 1.12 or 1.15 or 1.18 or 1.20 or 1.24 or 1.30
or 1.32 or 1.35 g/cc. In other instances, the outer skin may have a
specific gravity of less than 0.90 g/cc. For example, the specific
gravity of the outer skin (SG.sub.skin of inner core) may be about
0.75 or 0.80 or 0.82 or 0.85 or 0.88 g/cc. In such instances,
wherein both the (SG.sub.center of inner core) and (SG.sub.skin of
inner core) are less than 0.90 g/cc, it is still preferred that the
(SG.sub.center of inner core) be less than the (SG.sub.skin of
inner core).
[0090] Thermoset Materials
[0091] As discussed above, the inner core (center) is made
preferably from a foamed polyurethane composition. Preferably, a
two-layered or dual-core is made, wherein the inner core is
surrounded by an outer core layer. In one preferred embodiment, the
outer core layer is formed from a non-foamed thermoset composition
and more preferably from a non-foamed thermoset rubber
composition.
[0092] Suitable thermoset rubber materials that may be used to form
the outer core layer include, but are not limited to,
polybutadiene, polyisoprene, ethylene propylene rubber ("EPR"),
ethylene-propylene-diene ("EPDM") rubber, styrene-butadiene rubber,
styrenic block copolymer rubbers (such as "SI", "SIS", "SB", "SBS",
"SIBS", and the like, where "S" is styrene, "I" is isobutylene, and
"B" is butadiene), polyalkenamers such as, for example,
polyoctenamer, butyl rubber, halobutyl rubber, polystyrene
elastomers, polyethylene elastomers, polyurethane elastomers,
polyurea elastomers, metallocene-catalyzed elastomers and
plastomers, copolymers of isobutylene and p-alkylstyrene,
halogenated copolymers of isobutylene and p-alkylstyrene,
copolymers of butadiene with acrylonitrile, polychloroprene, alkyl
acrylate rubber, chlorinated isoprene rubber, acrylonitrile
chlorinated isoprene rubber, and blends of two or more thereof.
Preferably, the outer core layer is formed from a polybutadiene
rubber composition.
[0093] The thermoset rubber composition may be cured using
conventional curing processes. Suitable curing processes include,
for example, peroxide-curing, sulfur-curing, high-energy radiation,
and combinations thereof. Preferably, the rubber composition
contains a free-radical initiator selected from organic peroxides,
high energy radiation sources capable of generating free-radicals,
and combinations thereof. In one preferred version, the rubber
composition is peroxide-cured. Suitable organic peroxides include,
but are not limited to, dicumyl peroxide;
n-butyl-4,4-di(t-butylperoxy) valerate;
1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;
2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;
di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;
2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;
di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoyl
peroxide; t-butyl hydroperoxide; and combinations thereof. In a
particular embodiment, the free radical initiator is dicumyl
peroxide, including, but not limited to Perkadox.RTM. BC,
commercially available from Akzo Nobel. Peroxide free-radical
initiators are generally present in the rubber composition in an
amount of at least 0.05 parts by weight per 100 parts of the total
rubber, or an amount within the range having a lower limit of 0.05
parts or 0.1 parts or 1 part or 1.25 parts or 1.5 parts or 2.5
parts or 5 parts by weight per 100 parts of the total rubbers, and
an upper limit of 2.5 parts or 3 parts or 5 parts or 6 parts or 10
parts or 15 parts by weight per 100 parts of the total rubber.
Concentrations are in parts per hundred (phr) unless otherwise
indicated. As used herein, the term, "parts per hundred," also
known as "phr" or "pph" 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 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.
[0094] The rubber compositions may further include a reactive
cross-linking co-agent. Suitable co-agents include, but are not
limited to, metal salts of unsaturated carboxylic acids having from
3 to 8 carbon atoms; unsaturated vinyl compounds and polyfunctional
monomers (e.g., trimethylolpropane trimethacrylate); phenylene
bismaleimide; and combinations thereof. Particular examples of
suitable metal salts include, but are not limited to, one or more
metal salts of acrylates, diacrylates, methacrylates, and
dimethacrylates, wherein the metal is selected from magnesium,
calcium, zinc, aluminum, lithium, and nickel. In a particular
embodiment, the co-agent is selected from zinc salts of acrylates,
diacrylates, methacrylates, and dimethacrylates. In another
particular embodiment, the agent is zinc diacrylate (ZDA). When the
co-agent is zinc diacrylate and/or zinc dimethacrylate, the
co-agent is typically included in the rubber composition in an
amount within the range having a lower limit of 1 or 5 or 10 or 15
or 19 or 20 parts by weight per 100 parts of the total rubber, and
an upper limit of 24 or 25 or 30 or 35 or 40 or 45 or 50 or 60
parts by weight per 100 parts of the base rubber.
[0095] Radical scavengers such as a halogenated organosulfur,
organic disulfide, or inorganic disulfide compounds may be added to
the rubber composition. These compounds also may function as "soft
and fast agents." As used herein, "soft and fast agent" means any
compound or a blend thereof that is capable of making a core: 1)
softer (having a lower compression) at a constant "coefficient of
restitution" (COR); and/or 2) faster (having a higher COR at equal
compression), when compared to a core equivalently prepared without
a soft and fast agent. Preferred halogenated organosulfur compounds
include, but are not limited to, pentachlorothiophenol (PCTP) and
salts of PCTP such as zinc pentachlorothiophenol (ZnPCTP). Using
PCTP and ZnPCTP in golf ball inner cores helps produce softer and
faster inner cores. The PCTP and ZnPCTP compounds help increase the
resiliency and the coefficient of restitution of the core. In a
particular embodiment, the soft and fast agent is selected from
ZnPCTP, PCTP, ditolyl disulfide, diphenyl disulfide, dixylyl
disulfide, 2-nitroresorcinol, and combinations thereof.
[0096] The rubber composition also may include filler(s) such as
materials selected from carbon black, clay and nanoclay particles
as discussed above, talc (e.g., Luzenac HAR.RTM. high aspect ratio
talcs, commercially available from Luzenac America, Inc.), glass
(e.g., glass flake, milled glass, and microglass), mica and
mica-based pigments (e.g., Iriodin.RTM. pearl luster pigments,
commercially available from The Merck Group), and combinations
thereof. Metal fillers such as, for example, particulate; powders;
flakes; and fibers of copper, steel, brass, tungsten, titanium,
aluminum, magnesium, molybdenum, cobalt, nickel, iron, lead, tin,
zinc, barium, bismuth, bronze, silver, gold, and platinum, and
alloys and combinations thereof also may be added to the rubber
composition to adjust the specific gravity of the composition as
needed. As discussed further below, in one preferred embodiment,
the specific gravity of the inner core layer (for example, foamed
polyurethane) has a specific gravity less than the outer core layer
(for example, polybutadiene rubber). In such an event, if mineral,
metal, or other fillers are added to the polybutadiene rubber
composition used to form the outer core, it is important the
concentration of such fillers be sufficient so that the specific
gravity of the outer core layer is greater than the specific
gravity of the inner core. For example, the concentration of the
fillers may be in an amount of at least about 5% by weight based on
total weight of composition
[0097] In addition, the rubber compositions may include
antioxidants. Also, processing aids such as high molecular weight
organic acids and salts thereof may be added to the composition.
Suitable organic acids are aliphatic organic acids, aromatic
organic acids, saturated mono-functional organic acids, unsaturated
monofunctional organic acids, multi-unsaturated mono-functional
organic acids, and dimerized derivatives thereof. Particular
examples of suitable organic acids include, but are not limited to,
caproic acid, caprylic acid, capric acid, lauric acid, stearic
acid, behenic acid, erucic acid, oleic acid, linoleic acid,
myristic acid, benzoic acid, palmitic acid, phenylacetic acid,
naphthalenoic acid, and dimerized derivatives thereof. The organic
acids are aliphatic, mono-functional (saturated, unsaturated, or
multi-unsaturated) organic acids. Salts of these organic acids may
also be employed. The salts of organic acids include the salts of
barium, lithium, sodium, zinc, bismuth, chromium, cobalt, copper,
potassium, strontium, titanium, tungsten, magnesium, cesium, iron,
nickel, silver, aluminum, tin, or calcium, salts of fatty acids,
particularly stearic, behenic, erucic, oleic, linoelic or dimerized
derivatives thereof. It is preferred that the organic acids and
salts of the present invention be relatively non-migratory (they do
not bloom to the surface of the polymer under ambient temperatures)
and non-volatile (they do not volatilize at temperatures required
for melt-blending.) Other ingredients such as accelerators (for
example, tetra methylthiuram), processing aids, dyes and pigments,
wetting agents, surfactants, plasticizers, coloring agents,
fluorescent agents, chemical blowing and foaming agents, defoaming
agents, stabilizers, softening agents, impact modifiers,
antiozonants, as well as other additives known in the art may be
added to the rubber composition.
[0098] Examples of commercially-available polybutadiene rubbers
that can be used in accordance with this invention, include, but
are not limited to, BR 01 and BR 1220, available from BST
Elastomers of Bangkok, Thailand; SE BR 1220LA and SE BR1203,
available from DOW Chemical Co of Midland, Mich.; BUDENE 1207,
1207s, 1208, and 1280 available from Goodyear, Inc of Akron, Ohio;
BR 01, 51 and 730, available from Japan Synthetic Rubber (JSR) of
Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29 MES, CB
60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221, available
from Lanxess Corp. of Pittsburgh. Pa.; BR1208, available from LG
Chemical of Seoul, South Korea; UBEPOL BR130B, BR150, BR150B,
BR150L, BR230, BR360L, BR710, and VCR617, available from UBE
Industries, Ltd. of Tokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60
AF and P30AF, and EUROPRENE BR HV80, available from Polimeri Europa
of Rome, Italy; AFDENE 50 and NEODENE BR40, BR45, BR50 and BR60,
available from Karbochem (PTY) Ltd. of Bruma, South Africa; KBR 01,
NdBr 40, NdBR-45, NdBr 60, KBR 710S, KBR 710H, and KBR 750,
available from Kumho Petrochemical Co., Ltd. Of Seoul, South Korea;
and DIENE 55NF, 70AC, and 320 AC, available from Firestone Polymers
of Akron, Ohio.
[0099] The polybutadiene rubber is used in an amount of at least
about 5% by weight based on total weight of composition and is
generally present in an amount of about 5% to about 100%, or an
amount within a range having a lower limit of 5% or 10% or 20% or
30% or 40% or 50% and an upper limit of 55% or 60% or 70% or 80% or
90% or 95% or 100%. Preferably, the concentration of polybutadiene
rubber is about 40 to about 95 weight percent. If desirable, lesser
amounts of other thermoset materials may be incorporated into the
base rubber. Such materials include the rubbers discussed above,
for example, cis-polyisoprene, trans-polyisoprene, balata,
polychloroprene, polynorbornene, polyoctenamer, polypentenamer,
butyl rubber, EPR, EPDM, styrene-butadiene, and the like.
[0100] Thermoplastic Materials
[0101] As discussed above, in one preferred embodiment, a thermoset
rubber composition is used to form the outer core. In alternative
embodiments, the outer core layer is made from a thermoplastic
material, which is preferably non-foamed, for example, a non-foamed
ionomer composition.
[0102] Suitable ionomer compositions include partially-neutralized
ionomers and highly-neutralized ionomers (HNPs), including ionomers
formed from blends of two or more partially-neutralized ionomers,
blends of two or more highly-neutralized ionomers, and blends of
one or more partially-neutralized ionomers with one or more
highly-neutralized ionomers. For purposes of the present
disclosure, "HNP" refers to an acid copolymer after at least 70% of
all acid groups present in the composition are neutralized.
[0103] Preferred ionomers are salts of O/X- and O/X/Y-type acid
copolymers, wherein O is an .alpha.-olefin, X is a C.sub.3-C.sub.8
.alpha.,.beta.-ethylenically unsaturated carboxylic acid, and Y is
a softening monomer. O is preferably selected from ethylene and
propylene. X is preferably selected from methacrylic acid, acrylic
acid, ethacrylic acid, crotonic acid, and itaconic acid.
Methacrylic acid and acrylic acid are particularly preferred. Y is
preferably selected from (meth) acrylate and alkyl (meth) acrylates
wherein the alkyl groups have from 1 to 8 carbon atoms, including,
but not limited to, n-butyl (meth) acrylate, isobutyl (meth)
acrylate, methyl (meth) acrylate, and ethyl (meth) acrylate.
[0104] Preferred O/X and O/X/Y-type copolymers include, without
limitation, ethylene acid copolymers, such as
ethylene/(meth)acrylic acid, ethylene/(meth)acrylic acid/maleic
anhydride, ethylene/(meth)acrylic acid/maleic acid mono-ester,
ethylene/maleic acid, ethylene/maleic acid mono-ester,
ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,
ethylene/(meth)acrylic acid/iso-butyl (meth)acrylate,
ethylene/(meth)acrylic acid/methyl (meth)acrylate,
ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and
the like. The term, "copolymer," as used herein, includes polymers
having two types of monomers, those having three types of monomers,
and those having more than three types of monomers. Preferred
.alpha.,.beta.-ethylenically unsaturated mono- or dicarboxylic
acids are (meth) acrylic acid, ethacrylic acid, maleic acid,
crotonic acid, fumaric acid, itaconic acid. (Meth) acrylic acid is
most preferred. As used herein, "(meth) acrylic acid" means
methacrylic acid and/or acrylic acid. Likewise, "(meth) acrylate"
means methacrylate and/or acrylate.
[0105] In a particularly preferred version, highly neutralized E/X-
and E/X/Y-type acid copolymers, wherein E is ethylene, X is a
C.sub.3-C.sub.8 .alpha.,.beta.-ethylenically unsaturated carboxylic
acid, and Y is a softening monomer are used. X is preferably
selected from methacrylic acid, acrylic acid, ethacrylic acid,
crotonic acid, and itaconic acid. Methacrylic acid and acrylic acid
are particularly preferred. Y is preferably an acrylate selected
from alkyl acrylates and aryl acrylates and preferably selected
from (meth) acrylate and alkyl (meth) acrylates wherein the alkyl
groups have from 1 to 8 carbon atoms, including, but not limited
to, n-butyl (meth) acrylate, isobutyl (meth) acrylate, methyl
(meth) acrylate, and ethyl (meth) acrylate. Preferred E/X/Y-type
copolymers are those wherein X is (meth) acrylic acid and/or Y is
selected from (meth) acrylate, n-butyl (meth) acrylate, isobutyl
(meth) acrylate, methyl (meth) acrylate, and ethyl (meth) acrylate.
More preferred E/X/Y-type copolymers are ethylene/(meth) acrylic
acid/n-butyl acrylate, ethylene/(meth) acrylic acid/methyl
acrylate, and ethylene/(meth) acrylic acid/ethyl acrylate.
[0106] The amount of ethylene in the acid copolymer is typically at
least 15 wt. %, preferably at least 25 wt. %, more preferably least
40 wt. %, and even more preferably at least 60 wt. %, based on
total weight of the copolymer. The amount of C.sub.3 to C.sub.8
.alpha.,.beta.-ethylenically unsaturated mono- or dicarboxylic acid
in the acid copolymer is typically from 1 wt. % to 35 wt. %,
preferably from 5 wt. % to 30 wt. %, more preferably from 5 wt. %
to 25 wt. %, and even more preferably from 10 wt. % to 20 wt. %,
based on total weight of the copolymer. The amount of optional
softening comonomer in the acid copolymer is typically from 0 wt. %
to 50 wt. %, preferably from 5 wt. % to 40 wt. %, more preferably
from 10 wt. % to 35 wt. %, and even more preferably from 20 wt. %
to 30 wt. %, based on total weight of the copolymer. "Low acid" and
"high acid" ionomeric polymers, as well as blends of such ionomers,
may be used. In general, low acid ionomers are considered to be
those containing 16 wt. % or less of acid moieties, whereas high
acid ionomers are considered to be those containing greater than 16
wt. % of acid moieties.
[0107] The various O/X, E/X, O/X/Y, and E/X/Y-type copolymers are
at least partially neutralized with a cation source, optionally in
the presence of a high molecular weight organic acid, such as those
disclosed in U.S. Pat. No. 6,756,436, the entire disclosure of
which is hereby incorporated herein by reference. The acid
copolymer can be reacted with the optional high molecular weight
organic acid and the cation source simultaneously, or prior to the
addition of the cation source. Suitable cation sources include, but
are not limited to, metal ion sources, such as compounds of alkali
metals, alkaline earth metals, transition metals, and rare earth
elements; ammonium salts and monoamine salts; and combinations
thereof. Preferred cation sources are compounds of magnesium,
sodium, potassium, cesium, calcium, barium, manganese, copper,
zinc, lead, tin, aluminum, nickel, chromium, lithium, and rare
earth metals. The amount of cation used in the composition is
readily determined based on desired level of neutralization. As
discussed above, for HNP compositions, the acid groups are
neutralized to 70% or greater, preferably 70 to 100%, more
preferably 90 to 100%. In one embodiment, an excess amount of
neutralizing agent, that is, an amount greater than the
stoichiometric amount needed to neutralize the acid groups, may be
used. That is, the acid groups may be neutralized to 100% or
greater, for example 110% or 120% or greater. In other embodiments,
partially-neutralized compositions are prepared, wherein 10% or
greater, normally 30% or greater of the acid groups are
neutralized. When aluminum is used as the cation source, it is
preferably used at low levels with another cation such as zinc,
sodium, or lithium, since aluminum has a dramatic effect on melt
flow reduction and cannot be used alone at high levels. For
example, aluminum is used to neutralize about 10% of the acid
groups and sodium is added to neutralize an additional 90% of the
acid groups.
[0108] "Ionic plasticizers" such as organic acids or salts of
organic acids, particularly fatty acids, may be added to the
ionomer resin. Such ionic plasticizers are used to make
conventional ionomer composition more processable as described in
Rajagopalan et al., U.S. Pat. No. 6,756,436, the disclosure of
which is hereby incorporated by reference. In the present invention
such ionic plasticizers are optional. In one preferred embodiment,
a thermoplastic ionomer composition is made by neutralizing about
70 wt % or more of the acid groups without the use of any ionic
plasticizer. On the other hand, in some instances, it may be
desirable to add a small amount of ionic plasticizer, provided that
it does not adversely affect the heat-resistance properties of the
composition. For example, the ionic plasticizer may be added in an
amount of about 10 to about 50 weight percent (wt. %) of the
composition, more preferably 30 to 55 wt. %.
[0109] The organic acids may be aliphatic, mono- or
multi-functional (saturated, unsaturated, or multi-unsaturated)
organic acids. Salts of these organic acids may also be employed.
Suitable fatty acid salts include, for example, metal stearates,
laureates, oleates, palmitates, pelargonates, and the like. For
example, fatty acid salts such as zinc stearate, calcium stearate,
magnesium stearate, barium stearate, and the like can be used. The
salts of fatty acids are generally fatty acids neutralized with
metal ions. The metal cation salts provide the cations capable of
neutralizing (at varying levels) the carboxylic acid groups of the
fatty acids. Examples include the sulfate, carbonate, acetate and
hydroxide salts of metals such as barium, lithium, sodium, zinc,
bismuth, chromium, cobalt, copper, potassium, strontium, titanium,
tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin,
or calcium, and blends thereof. It is preferred the organic acids
and salts be relatively non-migratory (they do not bloom to the
surface of the polymer under ambient temperatures) and non-volatile
(they do not volatilize at temperatures required for
melt-blending).
[0110] Other suitable thermoplastic polymers that may be used to
form the inner cover layer include, but are not limited to, the
following polymers (including homopolymers, copolymers, and
derivatives thereof.) [0111] (a) polyesters, particularly those
modified with a compatibilizing group such as sulfonate or
phosphonate, including modified poly(ethylene terephthalate),
modified poly(butylene terephthalate), modified poly(propylene
terephthalate), modified poly(trimethylene terephthalate), modified
poly(ethylene naphthenate), and those disclosed in U.S. Pat. Nos.
6,353,050, 6,274,298, and 6,001,930, the entire disclosures of
which are hereby incorporated herein by reference, and blends of
two or more thereof; [0112] (b) polyamides, polyamide-ethers, and
polyamide-esters, and those disclosed in U.S. Pat. Nos. 6,187,864,
6,001,930, and 5,981,654, the entire disclosures of which are
hereby incorporated herein by reference, and blends of two or more
thereof; [0113] (c) polyurethanes, polyureas, polyurethane-polyurea
hybrids, and blends of two or more thereof; [0114] (d)
fluoropolymers, such as those disclosed in U.S. Pat. Nos.
5,691,066, 6,747,110 and 7,009,002, the entire disclosures of which
are hereby incorporated herein by reference, and blends of two or
more thereof; [0115] (e) polystyrenes, such as
poly(styrene-co-maleic anhydride), acrylonitrile-butadiene-styrene,
poly(styrene sulfonate), polyethylene styrene, and blends of two or
more thereof; [0116] (f) polyvinyl chlorides and grafted polyvinyl
chlorides, and blends of two or more thereof; [0117] (g)
polycarbonates, blends of
polycarbonate/acrylonitrile-butadiene-styrene, blends of
polycarbonate/polyurethane, blends of polycarbonate/polyester, and
blends of two or more thereof; [0118] (h) polyethers, such as
polyarylene ethers, polyphenylene oxides, block copolymers of
alkenyl aromatics with vinyl aromatics and polyamicesters, and
blends of two or more thereof; [0119] (i) polyimides,
polyetherketones, polyamideimides, and blends of two or more
thereof; and [0120] (j) polycarbonate/polyester copolymers and
blends.
[0121] It also is recognized that thermoplastic materials can be
"converted" into thermoset materials by cross-linking the polymer
chains so they form a network structure, and such cross-linked
thermoplastic materials may be used to form the inner cover layers
in accordance with this invention. For example, thermoplastic
polyolefins such as linear low density polyethylene (LLDPE), low
density polyethylene (LDPE), and high density polyethylene (HDPE)
may be cross-linked to form bonds between the polymer chains. The
cross-linked thermoplastic material typically has improved physical
properties and strength over non-cross-linked thermoplastics,
particularly at temperatures above the crystalline melting point.
Preferably a partially or fully-neutralized ionomer, as described
above, is covalently cross-linked to render it into a thermoset
composition (that is, it contains at least some level of covalent,
irreversable cross-links). Thermoplastic polyurethanes and
polyureas also may be converted into thermoset materials in
accordance with the present invention.
[0122] Modifications in the thermoplastic polymeric structure of
thermoplastics can be induced by a number of methods, including
exposing the thermoplastic material to high-energy radiation or
through a chemical process using peroxide. Radiation sources
include, but are not limited to, gamma-rays, electrons, neutrons,
protons, x-rays, helium nuclei, or the like. Gamma radiation,
typically using radioactive cobalt atoms and allows for
considerable depth of treatment, if necessary. For core layers
requiring lower depth of penetration, electron-beam accelerators or
UV and IR light sources can be used. Useful UV and IR irradiation
methods are disclosed in U.S. Pat. Nos. 6,855,070 and 7,198,576,
which are incorporated herein by reference. The thermoplastic core
layers may be irradiated at dosages greater than 0.05 Mrd,
preferably ranging from 1 Mrd to 20 Mrd, more preferably from 2 Mrd
to 15 Mrd, and most preferably from 4 Mrd to 10 Mrd. In one
preferred embodiment, the cores are irradiated at a dosage from 5
Mrd to 8 Mrd and in another preferred embodiment, the cores are
irradiated with a dosage from 0.05 Mrd to 3 Mrd, more preferably
0.05 Mrd to 1.5 Mrd.
[0123] The cross-linked thermoplastic material may be created by
exposing the thermoplastic to: 1) a high-energy radiation
treatment, such as electron beam or gamma radiation, such as
disclosed in U.S. Pat. No. 5,891,973, which is incorporated by
reference herein, 2) lower energy radiation, such as ultra-violet
(UV) or infra-red (IR) radiation; 3) a solution treatment, such as
an isocyanate or a silane; 4) incorporation of additional free
radical initiator groups in the thermoplastic prior to molding;
and/or 5) chemical modification, such as esterification or
saponification, to name a few.
[0124] Core Structure
[0125] As discussed above, the core of the golf ball of this
invention preferably has a dual-layered structure comprising an
inner core and outer core layer. Referring to FIG. 4, one version
of a four-piece golf ball that can be made in accordance with this
invention is generally indicated at (20). The ball (20) contains an
inner core (center) (22) and surrounding outer core layer (24). The
dual-core sub-assembly is encased by a multi-layered cover
comprising an inner cover (26) and outer cover (28). The inner core
(22) is relatively small in volume and generally has a diameter
within a range of about 0.10 to about 1.10 inches. More
particularly, the inner core (22) preferably has a diameter size
with a lower limit of about 0.15 or 0.25 or 0.35 or 0.45 or 0.55
inches and an upper limit of about 0.60 or 0.70 or 0.80 or 0.90
inches. In one preferred version, the diameter of the inner core
(22) is in the range of about 0.025 to about 0.080 inches, more
preferably about 0.030 to about 0.075 inches. Meanwhile, the outer
core layer (24) generally has a thickness within a range of about
0.010 to about 0.250 inches and preferably has a lower limit of
0.010 or 0.020 or 0.025 or 0.030 inches and an upper limit of 0.070
or 0.080 or 0.100 or 0.200 inches. In one preferred version, the
outer core layer has a thickness in the range of about 0.040 to
about 0.170 inches, more preferably about 0.060 to about 0.150
inches.
[0126] Referring to FIG. 5, in another version, a three-piece golf
ball (30) contains an inner core (center) (32) and outer core layer
(34). The dual-core sub-assembly is surrounded by a single-layered
cover (36).
[0127] The hardness of the core sub-assembly (inner core and outer
core layer) is an important property. In general, cores with
relatively high hardness values have higher compression and tend to
have good durability and resiliency. However, some high compression
balls are stiff and this may have a detrimental effect on shot
control and placement. Thus, the optimum balance of hardness in the
core sub-assembly needs to be attained.
[0128] In one preferred golf ball, the inner core (center) has a
"positive" hardness gradient (that is, the outer surface of the
inner core is harder than its geometric center); and the outer core
layer has a "positive" hardness gradient (that is, the outer
surface of the outer core layer is harder than the inner surface of
the outer core layer.) In such cases where both the inner core and
outer core layer each has a "positive" hardness gradient, the outer
surface hardness of the outer core layer is preferably greater than
the hardness of the geometric center of the inner core. In one
preferred version, the positive hardness gradient of the inner core
is in the range of about 2 to about 40 Shore C units and even more
preferably about 10 to about 25 Shore C units; while the positive
hardness gradient of the outer core is in the range of about 2 to
about 20 Shore C and even more preferably about 3 to about 10 Shore
C.
[0129] In an alternative version, the inner core may have a
positive hardness gradient; and the outer core layer may have a
"zero" hardness gradient (that is, the hardness values of the outer
surface of the outer core layer and the inner surface of the outer
core layer are substantially the same) or a "negative" hardness
gradient (that is, the outer surface of the outer core layer is
softer than the inner surface of the outer core layer.) For
example, in one version, the inner core has a positive hardness
gradient; and the outer core layer has a negative hardness gradient
in the range of about 2 to about 25 Shore C. In a second
alternative version, the inner core may have a zero or negative
hardness gradient; and the outer core layer may have a positive
hardness gradient. Still yet, in another embodiment, both the inner
core and outer core layers have zero or negative hardness
gradients.
[0130] In general, hardness gradients are further described in
Bulpett et al., U.S. Pat. Nos. 7,537,529 and 7,410,429, the
disclosures of which are hereby incorporated by reference. Methods
for measuring the hardness of the inner core and outer core layers
along with other layers in the golf ball and determining the
hardness gradients of the various layers are described in further
detail below. The core layers have positive, negative, or zero
hardness gradients defined by hardness measurements made at the
outer surface of the inner core (or outer surface of the outer core
layer) and radially inward towards the center of the inner core (or
inner surface of the outer core layer). These measurements are made
typically at 2-mm increments as described in the test methods
below. In general, the hardness gradient is determined by
subtracting the hardness value at the innermost portion of the
component being measured (for example, the center of the inner core
or inner surface of the outer core layer) from the hardness value
at the outer surface of the component being measured (for example,
the outer surface of the inner core or outer surface of the outer
core layer).
[0131] Positive Hardness Gradient. For example, if the hardness
value of the outer surface of the inner core is greater than the
hardness value of the inner core's geometric center (that is, the
inner core has a surface harder than its geometric center), the
hardness gradient will be deemed "positive" (a larger number minus
a smaller number equals a positive number.) For example, if the
outer surface of the inner core has a hardness of 67 Shore C and
the geometric center of the inner core has a hardness of 60 Shore
C, then the inner core has a positive hardness gradient of 7.
Likewise, if the outer surface of the outer core layer has a
greater hardness value than the inner surface of the outer core
layer, the given outer core layer will be considered to have a
positive hardness gradient.
[0132] Negative Hardness Gradient. On the other hand, if the
hardness value of the outer surface of the inner core is less than
the hardness value of the inner core's geometric center (that is,
the inner core has a surface softer than its geometric center), the
hardness gradient will be deemed "negative." For example, if the
outer surface of the inner core has a hardness of 68 Shore C and
the geometric center of the inner core has a hardness of 70 Shore
C, then the inner core has a negative hardness gradient of 2.
Likewise, if the outer surface of the outer core layer has a lesser
hardness value than the inner surface of the outer core layer, the
given outer core layer will be considered to have a negative
hardness gradient.
[0133] Zero Hardness Gradient. In another example, if the hardness
value of the outer surface of the inner core is substantially the
same as the hardness value of the inner core's geometric center
(that is, the surface of the inner core has about the same hardness
as the geometric center), the hardness gradient will be deemed
"zero." For example, if the outer surface of the inner core and the
geometric center of the inner core each has a hardness of 65 Shore
C, then the inner core has a zero hardness gradient. Likewise, if
the outer surface of the outer core layer has a hardness value
approximately the same as the inner surface of the outer core
layer, the outer core layer will be considered to have a zero
hardness gradient.
[0134] More particularly, the term, "positive hardness gradient" as
used herein means a hardness gradient of positive 3 Shore C or
greater, preferably 7 Shore C or greater, more preferably 10 Shore
C, and even more preferably 20 Shore C or greater. The term, "zero
hardness gradient" as used herein means a hardness gradient of less
than 3 Shore C, preferably less than 1 Shore C and may have a value
of zero or negative 1 to negative 10 Shore C. The term, "negative
hardness gradient" as used herein means a hardness value of less
than zero, for example, negative 3, negative 5, negative 7,
negative 10, negative 15, or negative 20 or negative 25. The terms,
"zero hardness gradient" and "negative hardness gradient" may be
used herein interchangeably to refer to hardness gradients of
negative 1 to negative 10.
[0135] The inner core preferably has a geometric center hardness
(H.sub.inner core center) of about 5 Shore D or greater. For
example, the (H.sub.inner core center) may be in the range of about
5 to about 88 Shore D and more particularly within a range having a
lower limit of about 5 or 10 or 18 or 20 or 26 or 30 or 34 or 36 or
38 or 42 or 48 or 50 or 52 Shore D and an upper limit of about 54
or 56 or 58 or 60 or 62 or 64 or 68 or 70 or 74 or 76 or 80 or 82
or 84 or 88 Shore D. In another example, the center hardness of the
inner core (H.sub.inner core center), as measured in Shore C units,
is preferably about 10 Shore C or greater; for example, the
H.sub.inner core center may have a lower limit of about 10 or 14 or
16 or 20 or 23 or 24 or 28 or 31 or 34 or 37 or 40 or 44 Shore C
and an upper limit of about 46 or 48 or 50 or 51 or 53 or 55 or 58
or 61 or 62 or 65 or 68 or 71 or 74 or 76 or 78 or 79 or 80 or 84
or 90 Shore C. Concerning the outer surface hardness of the inner
core (H.sub.inner core surface), this hardness is preferably about
12 Shore D or greater; for example, the H.sub.inner core surface
may fall within a range having a lower limit of about 12 or 15 or
18 or 20 or 22 or 26 or 30 or 34 or 36 or 38 or 42 or 48 or 50 or
52 Shore D and an upper limit of about 54 or 56 or 58 or 60 or 62
or 70 or 72 or 75 or 78 or 80 or 82 or 84 or 86 or 90 Shore D. In
one version, the outer surface hardness of the inner core
(H.sub.inner core surface), as measured in Shore C units, has a
lower limit of about 13 or 15 or 18 or 20 or 22 or 24 or 27 or 28
or 30 or 32 or 34 or 38 or 44 or 47 or 48 Shore C and an upper
limit of about 50 or 54 or 56 or 61 or 65 or 66 or 68 or 70 or 73
or 76 or 78 or 80 or 84 or 86 or 88 or 90 or 92 Shore C. In another
version, the geometric center hardness (H.sub.inner core center) is
in the range of about 10 Shore C to about 50 Shore C; and the outer
surface hardness of the inner core (H.sub.inner core surface) is in
the range of about 5 Shore C to about 50 Shore C.
[0136] On the other hand, the outer core layer preferably has an
outer surface hardness (H.sub.outer surface of OC) of about 40
Shore D or greater, and more preferably within a range having a
lower limit of about 40 or 42 or 44 or 46 or 48 or 50 or 52 and an
upper limit of about 54 or 56 or 58 or 60 or 62 or 64 or 70 or 74
or 78 or 80 or 82 or 85 or 87 or 88 or 90 Shore D. The outer
surface hardness of the outer core layer (H.sub.outer surface of
OC), as measured in Shore C units, preferably has a lower limit of
about 40 or 42 or 45 or 48 or 50 or 54 or 58 or 60 or 63 or 65 or
67 or 720 or 72 or 73 or 76 Shore C, and an upper limit of about 78
or 80 or 84 or 87 or 88 or 89 or 90 or 92 or 95 Shore C. And, the
inner surface of the outer core layer (H.sub.inner surface of OC)
or midpoint hardness of the outer core layer (H.sub.midpoint of
OC), preferably has a hardness of about 40 Shore D or greater, and
more preferably within a range having a lower limit of about 40 or
42 or 44 or 46 or 48 or 50 or 52 and an upper limit of about 54 or
56 or 58 or 60 or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or
87 or 88 or 90 Shore D. The inner surface hardness (H.sub.inner
surface of OC) or midpoint hardness (H.sub.midpoint of OC) of the
outer core layer, as measured in Shore C units, preferably has a
lower limit of about 40 or 42 or 44 or 45 or 47 or 50 or 52 or 54
or 55 or 58 or 60 or 63 or 65 or 67 or 70 or 73 or 75 Shore C, and
an upper limit of about 78 or 80 or 85 or 88 or 89 or 90 or 92 or
95 Shore C. Likewise, the midpoint of a core layer is taken at a
point equidistant from the inner surface and outer surface of the
layer to be measured, most typically an outer core layer. Once one
or more core layers surround a layer of interest, the exact
midpoint may be difficult to determine, therefore, for the purposes
of the present invention, the measurement of "midpoint" hardness of
a layer is taken within plus or minus 1 mm of the measured midpoint
of the layer.
[0137] In one embodiment, the outer surface hardness of the outer
core layer (H.sub.outer surface of OC), is less than the outer
surface hardness (H.sub.inner core surface) or midpoint hardness
(H.sub.midpoint of OC), of the inner core by at least 3 Shore C
units and more preferably by at least 5 Shore C.
[0138] In a second embodiment, the outer surface hardness of the
outer core layer (H.sub.outer surface of OC), is greater than the
outer surface hardness (H.sub.inner core surface) or midpoint
hardness (H.sub.midpoint of OC), of the inner core by at least 3
Shore C units and more preferably by at least 5 Shore C.
[0139] As discussed above, the inner core is preferably formed from
a foamed thermoplastic or thermoset composition and more preferably
foamed polyurethanes. And, the outer core layer is formed
preferably from a non-foamed thermoset composition such as
polybutadiene rubber. The outer core layer also may be formed from
non-foamed thermoplastic compositions.
[0140] The core structure also has a hardness gradient across the
entire core assembly. In one embodiment, the (H.sub.inner core
center) is in the range of about 10 Shore C to about 60 Shore C,
preferably about 13 Shore C to about 55 Shore C; and the
(H.sub.outer surface of OC) is in the range of about 65 to about 96
Shore C, preferably about 68 Shore C to about 94 Shore C or about
75 Shore C to about 93 Shore C, to provide a positive hardness
gradient across the core assembly. The gradient across the core
assembly will vary based on several factors including, but not
limited to, the dimensions of the inner core, intermediate core,
and outer core layers.
[0141] The inner core preferably has a diameter in the range of
about 0.100 to about 1.100 inches. For example, the inner core may
have a diameter within a range of about 0.100 to about 0.500
inches. In another example, the inner core may have a diameter
within a range of about 0.300 to about 0.800 inches. More
particularly, the inner core may have a diameter size with a lower
limit of about 0.10 or 0.12 or 0.15 or 0.25 or 0.30 or 0.35 or 0.45
or 0.55 inches and an upper limit of about 0.60 or 0.65 or 0.70 or
0.80 or 0.90 or 1.00 or 1.10 inches. As far as the outer core layer
is concerned, it preferably has a thickness in the range of about
0.100 to about 0.750 inches. For example, the lower limit of
thickness may be about 0.050 or 0.100 or 0.150 or 0.200 or 0.250 or
0.300 or 0.340 or 0.400 and the upper limit may be about 0.500 or
0.550 or 0.600 or 0.650 or 0.700 or 0.750 inches.
[0142] Dimensions--Thickness and Volume
[0143] Dual-layered core structures containing layers with various
thickness and volume levels may be made in accordance with this
invention. For example, in one version, the total diameter of the
core structure is 0.20 inches and the total volume of the core
structure is 0.23 cc. More particularly, in this example, the
diameter of the inner core is 0.10 inches and the volume of the
inner core is 0.10 cc; while the thickness of the outer core is
0.100 inches and the volume of the outer core is 0.13 cc. In
another version, the total core diameter is about 1.55 inches and
the total core volume is 31.96 cc. In this version, the outer core
layer has a thickness of 0.400 inches and volume of 28.34 cc.
Meanwhile, the inner core has a diameter of 0.75 inches and volume
of 3.62 cm. In one embodiment, the volume of the outer core layer
is greater than the volume of the inner core. In another
embodiment, the volume of the outer core layer and inner core are
equivalent. In still another embodiment, the volume of the outer
core layer is less than the volume of the inner core. Other
examples of core structures containing layers of varying
thicknesses and volumes are described below in Table A.
[0144] Table A--Sample Core Dimensions
TABLE-US-00001 TABLE A Sample Core Dimensions Thermoset Foamed
Volume Total Total Outer Outer Inner of Core Core Core Core Core
Inner Example Diameter Volume Thickness Volume Diameter Core A
0.30'' 0.23 cc 0.100'' 0.13 cc 0.10'' 0.10 cc B 1.60'' 33.15 cc
0.750'' 33.05 cc 0.10'' 0.10 cc C 1.55'' 31.96 cc 0.225'' 11.42 cc
1.10'' 11.42 cc D 1.55'' 31.96 cc 0.400'' 28.34 cc 0.75'' 3.62 cc E
1.55'' 31.96 cc 0.525'' 28.34 cc 0.50'' 3.62 cc
[0145] In one preferred embodiment, the inner core has a specific
gravity in the range of about 0.25 to about 1.25 g/cc. Also, as
discussed above, the specific gravity of the inner core may vary at
different points of the inner core structure. That is, there may be
a specific gravity gradient in the inner core. For example, in one
preferred version, the geometric center of the inner core has a
density in the range of about 0.25 to about 0.75 g/cc; while the
outer skin of the inner core has a density in the range of about
0.75 to about 1.50 g/cc.
[0146] Meanwhile, the outer core layer preferably has a relatively
high specific gravity. Thus, the specific gravity of the inner core
layer (SG.sub.inner) is preferably less than the specific gravity
of the outer core layer (SG.sub.outer). By the term, "specific
gravity of the outer core layer" ("SG.sub.outer"), it is generally
meant the specific gravity of the outer core layer as measured at
any point of the outer core layer. The specific gravity values at
different points in the outer core layer may vary. That is, there
may be specific gravity gradients in the outer core layer similar
to the inner core. For example, the outer core layer may have a
specific gravity within a range having a lower limit of about 0.50
or 0.60 or 0.70 or 0.75 or 0.85 or 0.95 or 1.00 or 1.10 or 1.25 or
1.30 or 1.36 or 1.40 or 1.42 or 1.48 or 1.50 or 1.60 or 1.66 or
1.75 or 2.00 and an upper limit of 2.50 or 2.60 or 2.80 or 2.90 or
3.00 or 3.10 or 3.25 or 3.50 or 3.60 or 3.80 or 4.00, 4.25 or 5.00
or 5.10 or 5.20 or 5.30 or 5.40 or 6.00 or 6.20 or 6.25 or 6.30 or
6.40 or 6.50 or 7.00 or 7.10 or 7.25 or 7.50 or 7.60 or 7.65 or
7.80 or 8.00 or 8.20 or 8.50 or 9.00 or 9.75 or 10.00 g/cc.
[0147] In general, the specific gravities of the respective pieces
of an object affect the Moment of Inertia (MOI) of the object. The
Moment of Inertia of a ball (or other object) about a given axis
generally refers to how difficult it is to change the ball's
angular motion about that axis. If the ball's mass is concentrated
towards the center (the center piece (for example, inner core) has
a higher specific gravity than the outer piece (for example, outer
core layers), less force is required to change its rotational rate,
and the ball has a relatively low Moment of Inertia. In such balls,
most of the mass is located close to the ball's axis of rotation
and less force is needed to generate spin. Thus, the ball has a
generally high spin rate as the ball leaves the club's face after
making impact. Conversely, if the ball's mass is concentrated
towards the outer surface (the outer piece (for example, outer core
layers) has a higher specific gravity than the center piece (for
example, inner core), more force is required to change its
rotational rate, and the ball has a relatively high Moment of
Inertia. That is, in such balls, most of the mass is located away
from the ball's axis of rotation and more force is needed to
generate spin. Such balls have a generally low spin rate as the
ball leaves the club's face after making impact.
[0148] More particularly, as described in Sullivan, U.S. Pat. No.
6,494,795 and Ladd et al., U.S. Pat. No. 7,651,415, the formula for
the Moment of Inertia for a sphere through any diameter is given in
the CRC Standard Mathematical Tables, 24th Edition, 1976 at 20
(hereinafter CRC reference). The term, "specific gravity" as used
herein, has its ordinary and customary meaning, that is, the ratio
of the density of a substance to the density of water at 4.degree.
C., and the density of water at this temperature is 1
g/cm.sup.3.
[0149] In one embodiment, the golf balls of this invention are
relatively low spin and long distance. That is, the foam core
construction, as described above, wherein the inner core is made of
a foamed composition helps provide a relatively low spin ball
having good resiliency. The inner foam cores of this invention
preferably have a Coefficient of Restitution (COR) of about 0.300
or greater; more preferably about 0.400 or greater, and even more
preferably about 0.450 or greater. The resulting balls containing
the dual-layered core constructions of this invention and cover of
at least one layer preferably have a COR of about 0.700 or greater,
more preferably about 0.730 or greater; and even more preferably
about 0.750 to 0.810 or greater. The inner foam cores preferably
have a Soft Center Deflection Index ("SCDI") compression, as
described in the Test Methods below, in the range of about 50 to
about 190, and more preferably in the range of about 60 to about
170.
[0150] The USGA has established a maximum weight of 45.93 g (1.62
ounces) for golf balls. For play outside of USGA rules, the golf
balls can be heavier. In one preferred embodiment, the weight of
the multi-layered core is in the range of about 28 to about 38
grams. Also, golf balls made in accordance with this invention can
be of any size, although the USGA requires that golf balls used in
competition have a diameter of at least 1.68 inches. For play
outside of United States Golf Association (USGA) rules, the golf
balls can be of a smaller size. Normally, golf balls are
manufactured in accordance with USGA requirements and have a
diameter in the range of about 1.68 to about 1.80 inches. As
discussed further below, the golf ball contains a cover which may
be multi-layered and in addition may contain intermediate (casing)
layers, and the thickness levels of these layers also must be
considered. Thus, in general, the dual-layer core structure
normally has an overall diameter within a range having a lower
limit of about 1.00 or 1.20 or 1.30 or 1.40 inches and an upper
limit of about 1.58 or 1.60 or 1.62 or 1.66 inches, and more
preferably in the range of about 1.3 to 1.65 inches. In one
embodiment, the diameter of the core sub-assembly is in the range
of about 1.45 to about 1.62 inches.
[0151] Cover Structure
[0152] The golf ball sub-assemblies of this invention may be
enclosed with one or more cover layers. The golf ball sub-assembly
may comprise the multi-layered core structure as discussed above.
In other versions, the golf ball sub-assembly includes the core
structure and one or more casing (mantle) layers disposed about the
core. In one particularly preferred version, the golf ball includes
a multi-layered cover comprising inner and outer cover layers. The
inner cover layer is preferably formed from a composition
comprising an ionomer or a blend of two or more ionomers that helps
impart hardness to the ball. In a particular embodiment, the inner
cover layer is formed from a composition comprising a high acid
ionomer. A particularly suitable high acid ionomer is Surlyn
8150.RTM. (DuPont). Surlyn 8150.RTM. is a copolymer of ethylene and
methacrylic acid, having an acid content of 19 wt %, which is 45%
neutralized with sodium. In another particular embodiment, the
inner cover layer is formed from a composition comprising a high
acid ionomer and a maleic anhydride-grafted non-ionomeric polymer.
A particularly suitable maleic anhydride-grafted polymer is
Fusabond 525D.RTM. (DuPont). Fusabond 525D.RTM. is a maleic
anhydride-grafted, metallocene-catalyzed ethylene-butene copolymer
having about 0.9 wt % maleic anhydride grafted onto the copolymer.
A particularly preferred blend of high acid ionomer and maleic
anhydride-grafted polymer is an 84 wt %/16 wt % blend of Surlyn
8150.RTM. and Fusabond 525D.RTM.. Blends of high acid ionomers with
maleic anhydride-grafted polymers are further disclosed, for
example, in U.S. Pat. Nos. 6,992,135 and 6,677,401, the entire
disclosures of which are hereby incorporated herein by
reference.
[0153] The inner cover layer also may be formed from a composition
comprising a 50/45/5 blend of Surlyn.RTM. 8940/Surlyn.RTM.
9650/Nucrel.RTM. 960, and, in a particularly preferred embodiment,
the composition has a material hardness of from 80 to 85 Shore C.
In yet another version, the inner cover layer is formed from a
composition comprising a 50/25/25 blend of Surlyn.RTM.
8940/Surlyn.RTM. 9650/Surlyn.RTM. 9910, preferably having a
material hardness of about 90 Shore C. The inner cover layer also
may be formed from a composition comprising a 50/50 blend of
Surlyn.RTM. 8940/Surlyn.RTM. 9650, preferably having a material
hardness of about 86 Shore C. A composition comprising a 50/50
blend of Surlyn.RTM. 8940 and Surlyn.RTM. 7940 also may be used.
Surlyn.RTM. 8940 is an E/MAA copolymer in which the MAA acid groups
have been partially neutralized with sodium ions. Surlyn.RTM. 9650
and Surlyn.RTM. 9910 are two different grades of E/MAA copolymer in
which the MAA acid groups have been partially neutralized with zinc
ions. Nucrel.RTM. 960 is an E/MAA copolymer resin nominally made
with 15 wt % methacrylic acid.
[0154] A wide variety of materials may be used for forming the
outer cover including, for example, polyurethanes; polyureas;
copolymers, blends and hybrids of polyurethane and polyurea;
olefin-based copolymer ionomer resins (for example, Surlyn.RTM.
ionomer resins and DuPont HPF.RTM. 1000 and HPF.RTM. 2000,
commercially available from DuPont; Iotek.RTM. ionomers,
commercially available from ExxonMobil Chemical Company;
Amplify.RTM. IO ionomers of ethylene acrylic acid copolymers,
commercially available from The Dow Chemical Company; and
Clarix.RTM. ionomer resins, commercially available from A. Schulman
Inc.); polyethylene, including, for example, low density
polyethylene, linear low density polyethylene, and high density
polyethylene; polypropylene; rubber-toughened olefin polymers; acid
copolymers, for example, poly(meth)acrylic acid, which do not
become part of an ionomeric copolymer; plastomers; flexomers;
styrene/butadiene/styrene block copolymers;
styrene/ethylene-butylene/styrene block copolymers; dynamically
vulcanized elastomers; copolymers of ethylene and vinyl acetates;
copolymers of ethylene and methyl acrylates; polyvinyl chloride
resins; polyamides, poly(amide-ester) elastomers, and graft
copolymers of ionomer and polyamide including, for example,
Pebax.RTM. thermoplastic polyether block amides, commercially
available from Arkema Inc; cross-linked trans-polyisoprene and
blends thereof; polyester-based thermoplastic elastomers, such as
Hytrel.RTM., commercially available from DuPont or RiteFlex.RTM.,
commercially available from Ticona Engineering Polymers;
polyurethane-based thermoplastic elastomers, such as
Elastollan.RTM., commercially available from BASF; synthetic or
natural vulcanized rubber; and combinations thereof. Castable
polyurethanes, polyureas, and hybrids of polyurethanes-polyureas
are particularly desirable because these materials can be used to
make a golf ball having high resiliency and a soft feel. By the
term, "hybrids of polyurethane and polyurea," it is meant to
include copolymers and blends thereof.
[0155] Polyurethanes, polyureas, and blends, copolymers, and
hybrids of polyurethane/polyurea are also particularly suitable for
forming cover layers. When used as cover layer materials,
polyurethanes and polyureas can be thermoset or thermoplastic.
Thermoset materials can be formed into golf ball layers by
conventional casting or reaction injection molding techniques.
Thermoplastic materials can be formed into golf ball layers by
conventional compression or injection molding techniques.
[0156] The compositions used to make the casing (mantle) and cover
layers may contain a wide variety of fillers and additives to
impart specific properties to the ball. For example, relatively
heavy-weight and light-weight metal fillers such as, particulate;
powders; flakes; and fibers of copper, steel, brass, tungsten,
titanium, aluminum, magnesium, molybdenum, cobalt, nickel, iron,
lead, tin, zinc, barium, bismuth, bronze, silver, gold, and
platinum, and alloys and combinations thereof may be used to adjust
the specific gravity of the ball. Other additives and fillers
include, but are not limited to, optical brighteners, coloring
agents, fluorescent agents, whitening agents, UV absorbers, light
stabilizers, surfactants, processing aids, antioxidants,
stabilizers, softening agents, fragrance components, plasticizers,
impact modifiers, titanium dioxide, clay, mica, talc, glass flakes,
milled glass, and mixtures thereof.
[0157] The inner cover layer preferably has a material hardness
within a range having a lower limit of 70 or 75 or 80 or 82 Shore C
and an upper limit of 85 or 86 or 90 or 92 Shore C. The thickness
of the intermediate layer is preferably within a range having a
lower limit of 0.010 or 0.015 or 0.020 or 0.030 inches and an upper
limit of 0.035 or 0.045 or 0.080 or 0.120 inches. The outer cover
layer preferably has a material hardness of 85 Shore C or less. The
thickness of the outer cover layer is preferably within a range
having a lower limit of 0.010 or 0.015 or 0.025 inches and an upper
limit of 0.035 or 0.040 or 0.055 or 0.080 inches. Methods for
measuring hardness of the layers in the golf ball are described in
further detail below.
[0158] A single cover or, preferably, an inner cover layer is
formed around the outer core layer. When an inner cover layer is
present, an outer cover layer is formed over the inner cover layer.
Most preferably, the inner cover is formed from an ionomeric
material and the outer cover layer is formed from a polyurethane
material, and the outer cover layer has a hardness that is less
than that of the inner cover layer. Preferably, the inner cover has
a hardness of greater than about 60 Shore D and the outer cover
layer has a hardness of less than about 60 Shore D. In an
alternative embodiment, the inner cover layer is comprised of a
partially or fully neutralized ionomer, a thermoplastic polyester
elastomer such as Hytrel.TM., commercially available form DuPont, a
thermoplastic polyether block amide, such as Pebax.TM.,
commercially available from Arkema,Inc., or a thermoplastic or
thermosetting polyurethane or polyurea, and the outer cover layer
is comprised of an ionomeric material. In this alternative
embodiment, the inner cover layer has a hardness of less than about
60 Shore D and the outer cover layer has a hardness of greater than
about 55 Shore D and the inner cover layer hardness is less than
the outer cover layer hardness.
[0159] As discussed above, the core structure of this invention may
be enclosed with one or more cover layers. In one embodiment, a
multi-layered cover comprising inner and outer cover layers is
formed, where the inner cover layer has a thickness of about 0.01
inches to about 0.06 inches, more preferably about 0.015 inches to
about 0.040 inches, and most preferably about 0.02 inches to about
0.035 inches. In this version, the inner cover layer is formed from
a partially- or fully-neutralized ionomer having a Shore D hardness
of greater than about 55, more preferably greater than about 60,
and most preferably greater than about 65. The outer cover layer,
in this embodiment, preferably has a thickness of about 0.015
inches to about 0.055 inches, more preferably about 0.02 inches to
about 0.04 inches, and most preferably about 0.025 inches to about
0.035 inches, with a hardness of about Shore D 80 or less, more
preferably 70 or less, and most preferably about 60 or less. The
inner cover layer is harder than the outer cover layer in this
version. A preferred outer cover layer is a castable or reaction
injection molded polyurethane, polyurea or copolymer, blend, or
hybrid thereof having a Shore D hardness of about 40 to about 50.
In another multi-layer cover, dual-core embodiment, the outer cover
and inner cover layer materials and thickness are the same but, the
hardness range is reversed, that is, the outer cover layer is
harder than the inner cover layer. For this harder outer
cover/softer inner cover embodiment, the ionomer resins described
above would preferably be used as outer cover material.
[0160] Manufacturing of Golf Balls
[0161] As described above, the inner core preferably is formed by
molding a foamed composition containing secondary heat-activated
blowing agents. The outer core layer, which surrounds the inner
core, is formed by molding a composition over the inner core. Then,
the casing and/or cover layers are applied over the core
sub-assembly. Prior to this step, the core structure may be
surface-treated to increase the adhesion between its outer surface
and the next layer that will be applied over the core. Such
surface-treatment may include mechanically or chemically-abrading
the outer surface of the core. For example, the core may be
subjected to corona-discharge, plasma-treatment, silane-dipping, or
other treatment methods known to those in the art.
[0162] The cover layers are formed over the core or ball
sub-assembly (the core structure and any casing layers disposed
about the core) using a suitable technique such as, for example,
compression-molding, flip-molding, injection-molding, retractable
pin injection-molding, reaction injection-molding (RIM), liquid
injection-molding, casting, spraying, powder-coating,
vacuum-forming, flow-coating, dipping, spin-coating, and the like.
Preferably, each cover layer is separately formed over the ball
subassembly. For example, an ethylene acid copolymer ionomer
composition may be injection-molded to produce half-shells.
Alternatively, the ionomer composition can be placed into a
compression mold and molded under sufficient pressure, temperature,
and time to produce the hemispherical shells. The smooth-surfaced
hemispherical shells are then placed around the core sub-assembly
in a compression mold. Under sufficient heating and pressure, the
shells fuse together to form an inner cover layer that surrounds
the sub-assembly. In another method, the ionomer composition is
injection-molded directly onto the core sub-assembly using
retractable pin injection molding. An outer cover layer comprising
a polyurethane or polyurea composition over the ball sub-assembly
may be formed by using a casting process.
[0163] After the golf balls have been removed from the mold, they
may be subjected to finishing steps such as flash-trimming,
surface-treatment, marking, coating, and the like using techniques
known in the art. For example, in traditional white-colored golf
balls, the white-pigmented cover may be surface-treated using a
suitable method such as, for example, corona, plasma, or
ultraviolet (UV) light-treatment. Then, indicia such as trademarks,
symbols, logos, letters, and the like may be printed on the ball's
cover using pad-printing, ink-jet printing, dye-sublimation, or
other suitable printing methods. Clear surface coatings (for
example, primer and top-coats), which may contain a fluorescent
whitening agent, are applied to the cover. The resulting golf ball
has a glossy and durable surface finish.
[0164] In another finishing process, the golf balls are painted
with one or more paint coatings. For example, white primer paint
may be applied first to the surface of the ball and then a white
top-coat of paint may be applied over the primer. Of course, the
golf ball may be painted with other colors, for example, red, blue,
orange, and yellow. As noted above, markings such as trademarks and
logos may be applied to the painted cover of the golf ball.
Finally, a clear surface coating may be applied to the cover to
provide a shiny appearance and protect any logos and other markings
printed on the ball. In FIG. 6, a finished golf ball (38) having a
dimpled outer cover (40) made in accordance with the present
invention is shown. As discussed above, various patterns and
geometric shapes of the dimples (40) can be used to modify the
aerodynamic properties of the golf ball.
[0165] Different ball constructions can be made using the methods
and core constructions of this invention as shown in FIGS. 1-6.
Such golf ball constructions include, for example, five-piece, and
six-piece constructions. It should be understood that the golf ball
components and finished golf balls shown in FIGS. 1-6 are for
illustrative purposes only, and they are not meant to be
restrictive. Other golf ball constructions can be made in
accordance with this invention. For example, the foam composition
of this invention is primarily discussed herein as being suitable
for producing a foam inner core or center for a golf ball. However,
it is recognized that this foam composition may be used for
producing an outer core layer, casing layer, cover, or any other
suitable component layer for the golf ball in accordance with this
invention.
[0166] Cores Having Three Layers
[0167] In another example, multi-layered cores having an inner
core, intermediate core layer, and outer core layer, wherein the
intermediate core layer is disposed between the intermediate and
outer core layers may be prepared in accordance with this
invention. More particularly, as discussed above, the inner core
may be constructed from a foamed composition, preferably foamed
polyurethane. Meanwhile, the intermediate and outer core layers may
be formed from non-foamed thermoset or thermoplastic materials.
Suitable thermoset and thermoplastic compositions that may be used
to form the intermediate/outer core layers are discussed above. For
example, each of the intermediate and outer core layers may be
formed from a thermoset rubber composition. Thus, the intermediate
core layer may be formed from a first thermoset rubber composition;
and the outer core layer may be formed from a second thermoset
rubber composition. In another embodiment, the intermediate core
layer is formed from a non-foamed thermoset composition; and the
outer core layer is formed from a non-foamed thermoplastic
composition. In a third embodiment, the intermediate core layer is
formed from a non-foamed thermoplastic composition; and the outer
core layer is formed from a non-foamed thermoset composition.
Finally, in a fourth embodiment, the intermediate core layer is
formed from a first non-foamed thermoplastic composition; and the
outer core layer is formed from a second non-foamed thermoplastic
compositions.
[0168] The above-discussed thermoset and thermoplastic compositions
may be used to form the intermediate and outer core layers. In one
embodiment, the specific gravity of the inner core (foamed
composition) is less than the specific gravity of the intermediate
and outer core layers. The specific gravities of the intermediate
and outer core layers may be the same or different. In one version,
the specific gravity of the intermediate core layer is greater than
the specific gravity of the outer core layer. In another version,
the specific gravity of the outer core is greater than the specific
gravity of the intermediate core layer.
[0169] Test Methods
[0170] Hardness. The center hardness of a core is obtained
according to the following procedure. The core is gently pressed
into a hemispherical holder having an internal diameter
approximately slightly smaller than the diameter of the core, such
that the core is held in place in the hemispherical portion of the
holder while concurrently leaving the geometric central plane of
the core exposed. The core is secured in the holder by friction,
such that it will not move during the cutting and grinding steps,
but the friction is not so excessive that distortion of the natural
shape of the core would result. The core is secured such that the
parting line of the core is roughly parallel to the top of the
holder. The diameter of the core is measured 90 degrees to this
orientation prior to securing. A measurement is also made from the
bottom of the holder to the top of the core to provide a reference
point for future calculations. A rough cut is made slightly above
the exposed geometric center of the core using a band saw or other
appropriate cutting tool, making sure that the core does not move
in the holder during this step. The remainder of the core, still in
the holder, is secured to the base plate of a surface grinding
machine. The exposed `rough` surface is ground to a smooth, flat
surface, revealing the geometric center of the core, which can be
verified by measuring the height from the bottom of the holder to
the exposed surface of the core, making sure that exactly half of
the original height of the core, as measured above, has been
removed to within 0.004 inches. Leaving the core in the holder, the
center of the core is found with a center square and carefully
marked and the hardness is measured at the center mark according to
ASTM D-2240. Additional hardness measurements at any distance from
the center of the core can then be made by drawing a line radially
outward from the center mark, and measuring the hardness at any
given distance along the line, typically in 2 mm increments from
the center. The hardness at a particular distance from the center
should be measured along at least two, preferably four, radial arms
located 180.degree. apart, or 90.degree. apart, respectively, and
then averaged. All hardness measurements performed on a plane
passing through the geometric center are performed while the core
is still in the holder and without having disturbed its
orientation, such that the test surface is constantly parallel to
the bottom of the holder, and thus also parallel to the properly
aligned foot of the durometer.
[0171] The outer surface hardness of a golf ball layer is measured
on the actual outer surface of the layer and is obtained from the
average of a number of measurements taken from opposing
hemispheres, taking care to avoid making measurements on the
parting line of the core or on surface defects, such as holes or
protrusions. Hardness measurements are made pursuant to ASTM D-2240
"Indentation Hardness of Rubber and Plastic by Means of a
Durometer." Because of the curved surface, care must be taken to
ensure that the golf ball or golf ball sub-assembly is centered
under the durometer indenter before a surface hardness reading is
obtained. A calibrated, digital durometer, capable of reading to
0.1 hardness units is used for the hardness measurements. The
digital durometer must be attached to, and its foot made parallel
to, the base of an automatic stand. The weight on the durometer and
attack rate conforms to ASTM D-2240.
[0172] In certain embodiments, a point or plurality of points
measured along the "positive" or "negative" gradients may be above
or below a line fit through the gradient and its outermost and
innermost hardness values. In an alternative preferred embodiment,
the hardest point along a particular steep "positive" or "negative"
gradient may be higher than the value at the innermost portion of
the inner core (the geometric center) or outer core layer (the
inner surface)--as long as the outermost point (i.e., the outer
surface of the inner core) is greater than (for "positive") or
lower than (for "negative") the innermost point (i.e., the
geometric center of the inner core or the inner surface of the
outer core layer), such that the "positive" and "negative"
gradients remain intact.
[0173] As discussed above, the direction of the hardness gradient
of a golf ball layer is defined by the difference in hardness
measurements taken at the outer and inner surfaces of a particular
layer. The center hardness of an inner core and hardness of the
outer surface of an inner core in a single-core ball or outer core
layer are readily determined according to the test procedures
provided above. The outer surface of the inner core layer (or other
optional intermediate core layers) in a dual-core ball are also
readily determined according to the procedures given herein for
measuring the outer surface hardness of a golf ball layer, if the
measurement is made prior to surrounding the layer with an
additional core layer. Once an additional core layer surrounds a
layer of interest, the hardness of the inner and outer surfaces of
any inner or intermediate layers can be difficult to determine.
Therefore, for purposes of the present invention, when the hardness
of the inner or outer surface of a core layer is needed after the
inner layer has been surrounded with another core layer, the test
procedure described above for measuring a point located 1 mm from
an interface is used. Likewise, the midpoint of a core layer is
taken at a point equidistant from the inner surface and outer
surface of the layer to be measured, most typically an outer core
layer. Once again, once one or more core layers surround a layer of
interest, the exact midpoint may be difficult to determine,
therefore, for the purposes of the present invention, the
measurement of "midpoint" hardness of a layer is taken within plus
or minus 1 mm of the measured midpoint of the layer.
[0174] Also, it should be understood that there is a fundamental
difference between "material hardness" and "hardness as measured
directly on a golf ball." For purposes of the present invention,
material hardness is measured according to ASTM D2240 and generally
involves measuring the hardness of a flat "slab" or "button" formed
of the material. Surface hardness as measured directly on a golf
ball (or other spherical surface) typically results in a different
hardness value. The difference in "surface hardness" and "material
hardness" values is due to several factors including, but not
limited to, ball construction (that is, core type, number of cores
and/or cover layers, and the like); ball (or sphere) diameter; and
the material composition of adjacent layers. It also should be
understood that the two measurement techniques are not linearly
related and, therefore, one hardness value cannot easily be
correlated to the other. Shore hardness (for example, Shore C or
Shore D hardness) was measured according to the test method ASTM
D-2240.
[0175] Compression. As disclosed in Jeff Dalton's Compression by
Any Other Name, Science and Golf IV, Proceedings of the World
Scientific Congress of Golf (Eric Thain ed., Routledge, 2002) ("J.
Dalton"), several different methods can be used to measure
compression, including Atti compression, Riehle compression,
load/deflection measurements at a variety of fixed loads and
offsets, and effective modulus. For purposes of the present
invention, compression refers to Soft Center Deflection Index
("SCDI"). The SCDI is a program change for the Dynamic Compression
Machine ("DCM") that allows determination of the pounds required to
deflect a core 10% of its diameter. The DCM is an apparatus that
applies a load to a core or ball and measures the number of inches
the core or ball is deflected at measured loads. A crude
load/deflection curve is generated that is fit to the Atti
compression scale that results in a number being generated that
represents an Atti compression. The DCM does this via a load cell
attached to the bottom of a hydraulic cylinder that is triggered
pneumatically at a fixed rate (typically about 1.0 ft/s) towards a
stationary core. Attached to the cylinder is an LVDT that measures
the distance the cylinder travels during the testing timeframe. A
software-based logarithmic algorithm ensures that measurements are
not taken until at least five successive increases in load are
detected during the initial phase of the test. The SCDI is a slight
variation of this set up. The hardware is the same, but the
software and output has changed. With the SCDI, the interest is in
the pounds of force required to deflect a core x amount of inches.
That amount of deflection is 10% percent of the core diameter. The
DCM is triggered, the cylinder deflects the core by 10% of its
diameter, and the DCM reports back the pounds of force required (as
measured from the attached load cell) to deflect the core by that
amount. The value displayed is a single number in units of
pounds.
[0176] Coefficient of Restitution ("COR"). The COR is determined
according to a known procedure, wherein a golf ball or golf ball
sub-assembly (for example, a golf ball core) is fired from an air
cannon at two given velocities and a velocity of 125 ft/s is used
for the calculations. Ballistic light screens are located between
the air cannon and steel plate at a fixed distance to measure ball
velocity. As the ball travels toward the steel plate, it activates
each light screen and the ball's time period at each light screen
is measured. This provides an incoming transit time period which is
inversely proportional to the ball's incoming velocity. The ball
makes impact with the steel plate and rebounds so it passes again
through the light screens. As the rebounding ball activates each
light screen, the ball's time period at each screen is measured.
This provides an outgoing transit time period which is inversely
proportional to the ball's outgoing velocity. The COR is then
calculated as the ratio of the ball's outgoing transit time period
to the ball's incoming transit time period
(COR=V.sub.out/V.sub.in=T.sub.in/T.sub.out).
[0177] Density. The density refers to the weight per unit volume
(typically, g/cm.sup.3) of the material and can be measured per
ASTM D-1622.
[0178] It is understood that the golf ball compositions,
constructions, and products described and illustrated herein
represent only some embodiments of the invention. It is appreciated
by those skilled in the art that various changes and additions can
be made to compositions, constructions, and products without
departing from the spirit and scope of this invention. It is
intended that all such embodiments be covered by the appended
claims.
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