U.S. patent application number 15/881790 was filed with the patent office on 2018-06-14 for golf balls having dual-layered cores with metal-containing centers and thermoplastic outer cores.
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, Michael J. Sullivan.
Application Number | 20180161633 15/881790 |
Document ID | / |
Family ID | 53881255 |
Filed Date | 2018-06-14 |
United States Patent
Application |
20180161633 |
Kind Code |
A1 |
Sullivan; Michael J. ; et
al. |
June 14, 2018 |
GOLF BALLS HAVING DUAL-LAYERED CORES WITH METAL-CONTAINING CENTERS
AND THERMOPLASTIC OUTER CORES
Abstract
Multi-piece golf balls containing a dual-layered core structure
are provided. The core structure includes a small, heavy inner core
(center) having a relatively high specific gravity, and a
surrounding outer core layer. The layers of the core structure may
have different hardness gradients. The center of the core comprises
a metal material such as copper, steel, brass, tungsten, titanium,
aluminum, and alloys thereof dispersed in a thermoset polymeric
matrix. The outer core layer is preferably formed from a
thermoplastic composition such as an ethylene acid copolymer
ionomer resin. The resulting ball has high resiliency and good
spin.
Inventors: |
Sullivan; Michael J.; (Old
Lyme, CT) ; Binette; Mark L.; (Mattapoisett,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Acushnet Company |
Fairhaven |
MA |
US |
|
|
Assignee: |
Acushnet Company
Fairhaven
MA
|
Family ID: |
53881255 |
Appl. No.: |
15/881790 |
Filed: |
January 28, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14711962 |
May 14, 2015 |
9878213 |
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15881790 |
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13606099 |
Sep 7, 2012 |
9095746 |
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14711962 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A63B 37/0064 20130101;
A63B 37/0063 20130101; A63B 37/0075 20130101; A63B 37/0033
20130101; A63B 37/0039 20130101; A63B 37/0054 20130101; A63B
37/0043 20130101; A63B 37/0066 20130101; A63B 37/0024 20130101;
A63B 37/0047 20130101; A63B 37/0076 20130101; A63B 37/0044
20130101; A63B 37/0092 20130101; A63B 37/0045 20130101 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Claims
1. A golf ball having a multi-layered core, comprising: i) an inner
core comprising a metal material dispersed in a thermoset polymeric
matrix, the inner core having a diameter in the range of about
0.100 to about 1.100 inches, a specific gravity (SG.sub.inner) of
1.60 to 6.25 g/cc, and an outer surface hardness (H.sub.center
surface) and a center hardness (H.sub.center material), the
H.sub.center surface being the same or less than the H.sub.center
material to provide a zero or negative hardness gradient; ii) an
outer core layer comprising a thermoplastic material, the outer
core layer being disposed about the inner core and having a
thickness in the range of about 0.200 to about 1.200 inches, a
specific gravity (SG.sub.outer), and an outer surface hardness
((H.sub.outer surface of OC) and an inner surface hardness
(H.sub.inner surface of OC), the H.sub.outer surface of OC being
greater than the H.sub.inner surface of OC to provide a positive
hardness gradient, wherein the SG.sub.inner is greater than the
SG.sub.outer, and the diameter of the inner core layer is less than
the thickness of the outer core layer; and iii) a cover having at
least one layer disposed about the multi-layered core.
2. The golf ball of claim 1, wherein the metal material of the
inner core is a metal selected from the group consisting of copper,
steel, brass, tungsten, titanium, aluminum, magnesium, molybdenum,
cobalt, nickel, iron, tin, bronze, silver, gold, and platinum, and
alloys and combinations thereof.
3. The golf ball of claim 1, wherein the inner core has a diameter
in the range of about 0.100 to about 0.500 inches.
4. The golf ball of claim 1, wherein the inner core has a diameter
in the range of about 0.30 to about 0.80 inches and specific
gravity in the range of about 1.80 to about 5.00 g/cc.
5. The golf ball of claim 1, wherein the H.sub.center material is
in the range of about 30 to about 62 Shore D and the H.sub.center
surface is in the range of about 26 to about 58 Shore D to provide
a zero or negative hardness gradient.
6. The golf ball of claim 1, wherein the outer core layer comprises
a thermoplastic material selected from the group consisting of
ethylene acid copolymer ionomers; polyesters; polyamides;
polyamide-ethers, polyamide-esters; polyurethanes, polyureas;
fluoropolymers; polystyrenes; polypropylenes and polyethylenes;
polyvinyl chlorides; polyvinyl acetates; polycarbonates; polyvinyl
alcohols; polyethers; polyimides, polyetherketones,
polyamideimides; and mixtures thereof.
7. The golf ball of claim 1, wherein the inner core comprises a
thermoset polymeric matrix comprises a thermoset rubber 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.
8. The golf ball of claim 7, wherein the thermoset rubber is
polybutadiene.
9. 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
specific gravity in the range of about 0.60 to about 4.10 g/cc.
10. The golf ball of claim 1, wherein the H.sub.outer surface of OC
is in the range of about 44 to about 90 Shore D and the H.sub.inner
surface of OC is in the range of about 40 to about 85 to provide a
positive hardness gradient.
11. The golf ball of claim 1, wherein the multi-layered core has a
specific gravity in the range of about 1.10 to about 5.75 g/cc.
12. The golf ball of claim 1, wherein the zero or negative hardness
gradient of the inner core is in the range of about 0 to about
negative 15 Shore D units.
13. The golf ball of claim 1, wherein the positive hardness
gradient of the outer core is in the range of about 3 to about 30
Shore D units.
14. The golf ball of claim 1, wherein the cover is a single layer
having a thickness of about 0.015 to about 0.090 inches and is
formed from a thermoplastic or thermoset material.
15. The golf ball of claim 1, wherein the cover comprises an inner
cover layer and outer cover layer, each cover having a surface
hardness, wherein the surface hardness of the inner cover layer is
greater than the surface hardness of the outer cover layer.
16. The golf ball of claim 1, wherein the cover comprises an inner
cover layer and outer cover layer, each cover having a surface
hardness, wherein the surface hardness of the outer cover layer is
greater than the surface hardness of the inner cover layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending,
co-assigned U.S. patent application Ser. No. 14/711,962, filed May
14, 2015, now allowed, which is a continuation-in-part of
co-assigned U.S. patent application Ser. No. 13/606,099, filed Sep.
7, 2012, now issued as U.S. Pat. No. 9,095,746 on Aug. 4, 2015, the
entire disclosures of which are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention generally relates to multi-piece golf
balls having a solid core of at least two layers and cover of at
least one layer. Preferably, the ball contains a dual-layered core
having a small, heavy inner core (center) and surrounding outer
core layer. The center comprises a metal material and the outer
core layer comprises a thermoplastic material such as an ethylene
acid copolymer ionomer. The core layers have different hardness
gradients and specific gravity values to provide finished balls
having high resiliency and spin-control properties.
Brief Review of the Related Art
[0003] Multi-piece, solid golf balls having a solid inner core
protected by a cover are used today by recreational and
professional golfers. The golf balls may have single-layered or
multi-layered cores. Normally, the core layers are made of a highly
resilient natural or synthetic rubber material such as styrene
butadiene, polybutadiene, poly(cis-isoprene), or
poly(trans-isoprene); or highly neutralized ethylene acid
copolymers (HNPs). The covers may be single or multi-layered and
made of a durable material such as HNPs, polyamides, polyesters,
polyurethanes, or polyureas. Manufacturers of golf balls use
different constructions (for example, three-piece, four-piece, and
five-piece balls) to impart specific properties and features to the
balls.
[0004] The core is the primary source of resiliency for the golf
ball and is often referred to as the "engine" of the ball. The
resiliency or coefficient of restitution ("COR") of a golf ball (or
golf ball component, particularly a core) means 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 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 the COR under these conditions. Balls
(or cores) with a high rebound velocity have a relatively high COR
value. Such golf balls rebound faster, retain more total energy
when struck with a club, and have longer flight distances as
opposed to balls with lower COR values. Ball resiliency and COR
properties are particularly important for long distance shots. For
example, balls having high resiliency and COR values tend to travel
a far distance when struck by a driver club from a tee. The spin
rate of the ball also is an important property. Balls having a
relatively high spin rate are particularly desirable for relatively
short distance shots made with irons and wedge clubs. Professional
and highly skilled recreational golfers can place a back-spin on
such balls more easily. By placing the right amount of spin and
touch on the ball, the golfer has better control over shot accuracy
and placement. This is particularly important for approach shots
near the green and helps improve scoring performance.
[0005] Over the years, golf ball manufacturers have looked at
adjusting the density or specific gravity among the multiple layers
of the golf ball to control its spin rate. In general, the total
weight of a golf ball has to conform to weight limits set by the
United States Golf Association ("USGA"). Although the total weight
of the golf ball is mandated, the distribution of weight within the
ball can vary. Redistributing the weight or mass of the golf ball
either towards the center of the ball or towards the outer surface
of the ball changes its flight and spin properties.
[0006] For example, the weight can be shifted towards the center of
the ball to increase the spin rate of the ball as described in
Yamada, U.S. Pat. No. 4,625,964. In the '964 Patent, the core
composition preferably contains 100 parts by weight of
polybutadiene rubber; 10 to 50 parts by weight of zinc acrylate or
zinc methacrylate; 10 to 150 parts by weight of zinc oxide; and 1
to 5 parts by weight of peroxide as a cross-linking or curing
agent. The inner core has a specific gravity of at least 1.50 in
order to make the spin rate of the ball comparable to wound balls.
The ball further includes a cover an intermediate layer disposed
between the core and cover, wherein the intermediate layer has a
lower specific gravity than the core.
[0007] Chikaraishi et al., U.S. Pat. No. 5,048,838 discloses a
three-piece golf ball containing a two-piece solid core and a
cover. The inner core has a diameter in the range of 15-25 mm, a
weight of 2-14 grams, a specific gravity of 1.2 to 4.0, and a
hardness of 55-80 JISC. The specific gravity of the outer core
layer is less than the specific gravity of the inner core by 0.1 to
3.0. less than the specific gravity of the inner core. The inner
and outer core layers are formed from rubber compositions.
[0008] Gentiluomo, U.S. Pat. No. 5,104,126 discloses a three-piece
ball with a dense inner core made of steel, lead, brass, zinc,
copper, and a filled elastomer, wherein the core has a specific
gravity of at least 1.25. The inner core is encapsulated by a lower
density syntactic foam composition, and the core construction is
encapsulated by an ionomer cover.
[0009] Yabuki et al., U.S. Pat. No. 5,482,285 discloses a
three-piece golf ball having an inner core and outer core
encapsulated by an ionomer cover. The specific gravity of the outer
core is reduced so that it falls within the range of 0.2 to 1.0.
The specific gravity of the inner core is adjusted so that the
total weight of the inner/outer core falls within a range of 32.0
to 39.0 g.
[0010] Nesbitt and Binette, U.S. Pat. No. 6,277,934 disclose a
non-wound, multi-piece golf ball containing a spherical metal core
component having a specific gravity of about 1.5 to about 19.4; and
an outer core layer disposed about said spherical metal core
component, wherein the core layer has a specific gravity of less
than 1.2. The metal core is preferably contains a metal selected
from steel, titanium, brass, lead, tungsten, molybdenum, copper,
nickel, iron, and combinations thereof. Polybutadiene rubber
compositions containing metallic powders can be used to form the
core. The core assembly preferably has a coefficient of restitution
of at least 0.730.
[0011] Sullivan, U.S. Pat. No. 6,494,795 discloses a golf ball
comprising an inner core having a specific gravity of greater than
1.8 encased within a first mantle surrounding the inner core. A
portion of the first mantle comprises a low specific gravity layer
having a specific gravity of less than 0.9. The core may be made
from a high density metal or from metal powder encased in a
polymeric binder. High density metals such as steel, tungsten,
lead, brass, bronze, copper, nickel, molybdenum, or alloys may be
used. The mantle layer surrounding the inner core may be made from
a thermoset or thermoplastic material such as epoxy, urethane,
polyester, polyurethane, or polyurea.
[0012] Sullivan, U.S. Pat. No. 6,692,380 discloses a golf ball
comprising an inner core having a specific gravity of at least 3, a
diameter of about 0.40 to about 0.60 inches and preferably
comprises a polymeric matrix of polyurethane, polyurea, or blends
thereof. The outer core may be made from a polybutadiene rubber.
The specific gravity of the compositions may be adjusted by adding
fillers such as metal powder, metal alloy powder, metal oxide,
metal stearates, particulates, and carbonaceous material.
[0013] Morgan and Jones, U.S. Pat. No. 6,986,717 discloses a golf
ball containing a high-specific gravity central sphere encapsulated
in a soft and resilient shell, preferably formed of a polybutadiene
rubber. This shell is subsequently wound with thread that is
preferably elastic to form a wound core. This wound core is then
covered with a cover material such as balata, gutta percha, an
ionomer or a blend of ionomers, polyurethane, polyurea-based
composition, and epoxy-urethane-based compositions. The sphere is
formed of metallic powder and a thermoset or thermoplastic binder
material. Metals such as tungsten, steel, brass, titanium, lead,
zinc, copper, bismuth, nickel, molybdenum, iron, bronze, cobalt,
silver, platinum, and gold can be used. Preferably, the metal
sphere has a specific gravity of at least 6.0 and a diameter of
less than 0.5 inches.
[0014] Although some conventional multi-layered core constructions
are generally effective in providing high resiliency golf balls,
there is a continuing need for improved core constructions in golf
balls. Particularly, it would be desirable to have multi-layered
core constructions with selective specific gravities and mass
densities to provide the ball with good flight distance along with
spin control. The present invention provides core constructions and
golf balls having such properties as well as other advantageous
features, and benefits.
SUMMARY OF THE INVENTION
[0015] The present invention provides a multi-piece golf ball
comprising a solid core having at least one layer and a cover
having at least one layer. The golf ball may have different
constructions. For example, in one embodiment, the golf ball
comprises: i) an inner core (center) comprising a metal material
and having a diameter of about 0.100 to about 1.100 inches and an
outer surface hardness (H.sub.center surface) and a center hardness
(H.sub.center material), wherein the H.sub.center surface is
greater than the H.sub.center material so that the inner core has a
positive hardness gradient; and ii) an outer core layer comprising
a thermoplastic material such as an ethylene acid copolymer ionomer
and having a thickness of about 0.200 to about 1.200 inches and an
outer surface hardness (H.sub.outer surface of OC) of 40 to 85
Shore D and an inner surface hardness (H.sub.inner surface of OC)
of 42 to 87 Shore D, wherein the (H.sub.outer surface of OC) is the
same or less than the (H.sub.inner surface of OC) so that the outer
core has a zero or negative hardness gradient and the specific
gravity of the inner core (SG.sub.inner) is greater than the
specific gravity of the outer core (SG.sub.outer) and diameter of
the inner core layer is less than the thickness of the outer core
layer. In one version, the positive hardness gradient of the inner
core is about 3 to about 20 Shore D units. In another version, the
zero or negative hardness gradient of the outer core is about 0 to
about negative 15 Shore D units. Also, in one example, the
multi-layered core a specific gravity of 1.10 to 5.75 g/cc.
[0016] The inner core may contain a metal such as copper, steel,
brass, tungsten, aluminum, magnesium, molybdenum, cobalt, nickel,
iron, tin, bronze, silver, gold, and platinum, and alloys and
combinations thereof. In one version, the inner core has a diameter
of about 0.100 to about 0.500 inches, a specific gravity of about
1.60 to about 6.25 g/cc, and a center hardness (H.sub.center
material) of about 44 to about 74 Shore D. In another version, the
diameter of the inner core is about 0.30 to about 0.80 inches and
the specific gravity is about 1.80 to about 5.00 g/cc. In one
version, the outer core has a thickness of about 0.250 to about
0.750 inches, a specific gravity of about 0.60 to about 4.10 g/cc,
and an outer surface hardness (H.sub.outer surface of OC) of about
40 to about 70 Shore D.
[0017] Also, the golf ball may have a variety of cover structures.
For example, the cover may be a single layer having a thickness of
about 0.15 to about 0.090 inches and be formed from a thermoplastic
or thermoset composition. In another embodiment, the cover includes
inner and outer cover layers. The surface hardness of the outer
cover may be harder or softer than the surface hardness of the
inner layer.
[0018] In another version, the golf ball contains a multi-layered
core comprising a metal-containing inner core having a positive
hardness gradient and a thermoplastic outer core layer having a
positive hardness gradient. Alternatively, in another version, the
golf ball may contain a multi-layered core comprising a
metal-containing inner core having a zero or negative hardness
gradient and a thermoplastic outer core layer having a zero or
negative hardness gradient. In yet another version, the golf ball
may contain a multi-layered core comprising a metal-containing
inner core having a zero or negative hardness gradient and a
thermoplastic outer core layer having a positive hardness gradient.
In each of these examples, the specific gravity of the inner core
preferably is greater than the specific gravity of the outer core
layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] 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:
[0020] FIG. 1 is a cross-sectional view of a three-piece golf ball
having a dual-layered core made in accordance with the present
invention; and
[0021] FIG. 2 is a cross-sectional view of a four-piece golf ball
having a dual-layered core made in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] Golf Ball Constructions
[0023] 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. 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 having a
dual-core and cover is made. The dual-core includes an inner core
(center) and surrounding outer core layer. In another version, a
four-piece golf ball comprising 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 having a multi-layered core;
an intermediate (casing) layer, and cover layer(s) may be made. As
used herein, the term, "intermediate layer" means a layer of the
ball disposed between the core and cover. The intermediate layer
also may be referred to as a casing or mantle 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.
[0024] Referring to FIG. 1, one version of a golf ball that can be
made in accordance with this invention is generally indicated at
(12). The ball (12) contains a multi-layered core (14) having an
inner core (center) (14a) and outer core layer (14b) surrounded by
a single-layered cover (16). The inner core (14a) 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
(14a) 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 (14a) 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 (14b) 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. Referring to FIG. 2,
in another version, the golf ball (18) contains a dual-core (20)
having an inner core (center) (20a) and outer core layer (20b). The
dual-core (20) is surrounded by a multi-layered cover (22) having
an inner cover layer (22a) and outer cover layer (22b).
[0025] 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. In
general, the multi-layer core structure (14) 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
subassembly (14) is in the range of about 1.45 to about 1.62
inches.
[0026] As discussed further below, various compositions may be used
to make the dual-core structures of the golf balls of this
invention. The golf balls may contain certain fillers to adjust the
specific gravity and weight of the core layers as needed. In
general, the inner core (center) has a specific gravity within a
range having a lower limit of about 1.18 or 1.50 or 2.00 or 2.50
g/cc and an upper limit of about 3.00 or 3.50 or 4.00 or 4.50 or
5.00 g/cc. In a preferred embodiment, the inner core has a specific
gravity of about 1.20 to about 3.50 g/cc, more preferably about
1.25 to about 3.00 g/cc. Meanwhile, the outer core layer (14b)
preferably has a relatively low specific gravity. The outer core
layer (14b) generally has a specific gravity within a range having
a lower limit of about 0.080 or 0.100 or 0.400 or 0.600 or 0.800
g/cc and an upper limit of about 1.00 or 1.10 or 1.20 g/cc. The
amount of fillers used in the compositions is adjusted so the
weight of the golf ball does not exceed limits set by USGA rules.
The USGA has established a maximum weight of 45.93 g (1.62 ounces).
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.
[0027] Core Structure
[0028] As discussed above, the core preferably has a dual-layered
structure comprising an inner core and surrounding outer core
layer. The hardness of the core subassembly 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. For example, some of
these harder balls tend to have a low spin rate and this makes the
ball more difficult to control. This can be particularly troubling
when making approach shots near the green. Thus, the optimum
balance of hardness in the core subassembly needs to be
attained.
[0029] 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 have "positive" hardness gradients, the outer
surface hardness of the outer core layer is preferably greater than
the material hardness of the inner core (center). 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.)
[0030] In another version, the inner core (center) has a zero or
negative hardness gradient, while the outer core layer has a
positive hardness gradient. In yet another version, both the inner
core and outer core layer have a zero or negative hardness
gradient. Such 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 layers are described in further detail below.
[0031] 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 inner 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).
[0032] 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 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 58 Shore D and the center of
the inner core has a hardness of 50 Shore D, then the inner core
has a positive hardness gradient of 8. 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 outer core layer
will be considered to have a positive hardness gradient.
[0033] 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 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
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 outer core
layer will be considered to have a negative hardness gradient.
[0034] 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 center), the hardness gradient will be deemed "zero." For
example, if the outer surface of the inner core and the center of
the inner core 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.
[0035] More particularly, the term, "positive hardness gradient" as
used herein means a hardness gradient of positive 3 Shore D or
greater, preferably 7 Shore D or greater, more preferably 10 Shore
D, and even more preferably 20 Shore D or greater. The term, "zero
hardness gradient" as used herein means a hardness gradient of less
than 3 Shore D, preferably less than 1 Shore D and may have a value
of zero or negative 1 to negative 10 Shore D. 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.
[0036] The inner core (center) preferably has a geometric center
hardness (H.sub.center material) of about 25 Shore D or greater and
more preferably within a range having a lower limit of about 26 or
30 or 34 or 36 or 38 or 42 or 48 of 50 or 52 Shore D and an upper
limit of about 54 or 56 or 58 or 60 or 62 Shore D. The center
hardness (H.sub.center material) of the inner core, as measured in
Shore C units, preferably has a lower limit of about 38 or 44 or 52
or 58 or 60 or 70 or 74 Shore C and an upper limit of about 76 or
78 or 80 or 84 or 86 or 88 or 90 or 92 Shore C. Concerning the
outer surface hardness (H.sub.center surface) of the inner core,
this hardness is preferably about 25 Shore D or greater. and more
preferably within a range having a lower limit of about about 26 or
30 or 34 or 36 or 38 or 42 or 48 of 50 or 52 Shore D and an upper
limit of about 54 or 56 or 58 or 60 or 62 Shore D.
[0037] Meanwhile, 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 63 or 65 or 67
or 70 or 73 or 76 Shore C, and an upper limit of about 78 or 80 or
85 or 87 or 89 or 90 or 92 or 95 Shore C, And, the inner surface of
the outer core (H.sub.inner surface of the 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.
[0038] Inner Core Composition
[0039] Preferably, the inner core composition comprises a metal
material such as, for example, copper, steel, brass, tungsten,
titanium, aluminum, magnesium, molybdenum, cobalt, nickel, iron,
lead, tin, bronze, silver, gold, and platinum, and alloys and
combinations thereof. The metal material may be dispersed in a
polymeric matrix, preferably a thermoset rubber material. The metal
material is dispersed uniformly in the polymeric matrix to provide
a substantially homogenous composition. The metal material is
blended fully into the polymeric matrix to prevent agglomerates and
aggregates from being formed. The resulting metal-containing
composition is used to form an inner core structure having a
relatively high specific gravity, thereby providing a ball having a
lower moment of inertia as discussed further below.
[0040] Suitable thermoset rubber materials that may be used as the
polymeric binder (matrix) material are natural and synthetic
rubbers including, but 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.
[0041] Preferably, the rubber composition comprises polybutadiene.
In general, polybutadiene is a homopolymer of 1, 3-butadiene. The
double bonds in the 1, 3-butadiene monomer are attacked by
catalysts to grow the polymer chain and form a polybutadiene
polymer having a desired molecular weight. Any suitable catalyst
may be used to synthesize the polybutadiene rubber depending upon
the desired properties. Normally, a transition metal complex (for
example, neodymium, nickel, or cobalt) or an alkyl metal such as
alkyllithium is used as a catalyst. Other catalysts include, but
are not limited to, aluminum, boron, lithium, titanium, and
combinations thereof. The catalysts produce polybutadiene rubbers
having different chemical structures. In a cis-bond configuration,
the main internal polymer chain of the polybutadiene appears on the
same side of the carbon-carbon double bond contained in the
polybutadiene. In a trans-bond configuration, the main internal
polymer chain is on opposite sides of the internal carbon-carbon
double bond in the polybutadiene. The polybutadiene rubber can have
various combinations of cis- and trans-bond structures. A preferred
polybutadiene rubber has a 1, 4 cis-bond content of at least 40%,
preferably greater than 80%, and more preferably greater than 90%.
In general, polybutadiene rubbers having a high 1, 4 cis-bond
content have high tensile strength. The polybutadiene rubber may
have a relatively high or low Mooney viscosity.
[0042] 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;
DIENE 55NF, 70AC, and 320 AC, available from Firestone Polymers of
Akron, Ohio; and PBR-Nd Group II and Group III, available from
Nizhnekamskneftekhim, Inc. of Nizhnekamsk, Tartarstan Republic.
[0043] 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. In other
versions, polybutadiene rubber is not used to form the polymeric
matrix. Rather, a different thermoset material is used.
[0044] In yet another version, a thermoplastic material may be used
as the polymeric binder (matrix) in the composition for making the
inner core. The thermoplastic material may be used as the polymeric
matrix for the metal material. These thermoplastic polymers
include, for example, ethylene acid copolymers containing acid
groups that are at least partially neutralized. Preferably, the
neutralization level is greater than 70%, more preferably at least
90%, and even more preferably at least 100%. Such ethylene acid
copolymers having a neutralization level of 70% or greater are
commonly referred to as highly neutralized polymers (HNPs).
Suitable ethylene acid copolymers that may be used to form the
compositions of this invention are generally referred to as
copolymers of ethylene; C.sub.3 to C.sub.8 .alpha.,
.beta.-ethylenically unsaturated mono- or dicarboxylic acid; and
optional softening monomer. Copolymers may 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. Other thermoplastics such as polyamides,
polyamide-ethers, and polyamide-esters, polyurethanes, polyureas,
polyurethane-polyurea hybrids, polyesters, polyolefins,
polystyrenes, and blends thereof may be used.
[0045] As discussed above, the composition used to form the inner
core contains a metal material. In one version, the metal material
can constitute the entire inner core. That is, the metal material
comprises 100% of the composition used to make the inner core. The
metal material is preferably in the shape of a solid sphere, for
example, a ball bearing. The metal sphere can be used as the inner
core (center) and a polymeric outer core layer can be disposed
about the metal center. Alternatively, metal fillers, as described
further below, can be dispersed in a polymeric binder to form a
metal-containing composition that can be used to make the inner
core. Relatively heavy-weight metal materials such as, for example,
a metal selected from the group consisting of copper, nickel,
tungsten, brass, steel, magnesium, molybdenum, cobalt, lead, tin,
silver, gold and platinum alloys can be used. Suitable steel
materials include, for example, chrome steel, stainless steel,
carbon steel, and alloys thereof. Alternatively, or in addition to
the heavy metals, relatively light-weight metal materials such as
titanium and aluminum alloys can be used, provided the inner core
layer has the required specific gravity. The metal filler is added
to the composition in a sufficient amount to obtain the desired
specific gravity as discussed further below.
[0046] If the size of the inner core (center) is small and a dense
metal material such as tungsten is being used, then the amount of
tungsten needed to obtain the desired specific gravity will be
relatively low. The weight of such a dense metal material is more
concentrated so a smaller amount of material is needed. On the
other hand, if a low density metal material such as aluminum is
being used, then the amount of aluminum needed to reach the needed
specific gravity will be relatively high. Normally, the metal
filler is present in the composition in an amount with the range of
about 1% to about 60%. Preferably, the metal filler is present in
the composition in an amount of 20 wt. % or less, 15 wt % or less,
or 12 wt % or less, or 10 wt % or less, or 6 wt % or less, or 4 wt
% or less based on weight of polymer in the composition.
[0047] The overall specific gravity of the core structure (inner
core and outer core layers) is preferably at least 1.8 g/cc, more
preferably at least 2.00 g/cc, and most preferably at least 2.50
g/cc. In general, the inner core has a specific gravity of at least
about 1.00 g/cc and is generally within the range of about 1.00 to
about 20.00. Preferably, the inner core has a lower limit of
specific gravity of about 1.10 or 1.20 or 1.50 or 2.00 or 2.50 or
3.50 or 4.00 or 5.00 or 6.00 or 7.00 or 8.00 g/cc and an upper
limit of about 9.00 or 9.50 or 10.00 or 10.50 or 11.00 or 12.00 or
13.00 or 14.00 or 15.00 or 16.00 or 17.00 or 18.00 or 19.00 or
19.50 g/cc. In a preferred embodiment, the inner core has a
specific gravity of about 1.20 to about 5.50 g/cc, more preferably
about 1.25 to about 3.25 g/cc.
[0048] Meanwhile, the outer core layer preferably has a relatively
low specific gravity. Thus, the specific gravity of inner core
layer (SG.sub.inner) is preferably greater than the specific
gravity of the outer core layer (SG.sub.outer). For example, the
outer core layer may have a specific gravity within a range having
a lower limit of about 0.80, 0.90 g/cc, 1.00 or 1.25 or 2.00 or
2.50 or 3.00 or 3.50 or 4.00, 4.25 or 5.00 and an upper limit of
about 6.00 or 6.50 or 7.00 or 7.25 or 8.00 or 8.50 or 9.00 or 9.25
or 10.00 g/cc. In one preferred embodiment, the SG.sub.inner is
preferably greater than the SG.sub.outer by at least 0.5 g/cc, more
preferably 0.75 g/cc or greater, and even more preferably 1.00 g/cc
or greater. In one embodiment, the difference between the
SG.sub.inner and the SG.sub.outer is within the range of about 0.5
g/cc to about 2.0 g/cc.
[0049] Suitable metal fillers that can be added to the polymeric
matrix used to form the inner core preferably have specific gravity
values in the range from about 1.5 to about 19.5, and include, for
example, metal (or metal alloy) powder, metal oxide, metal
stearates, particulates, flakes, and the like, and blends thereof.
Examples of useful metal (or metal alloy) powders include, but are
not limited to, bismuth powder, boron powder, brass powder, bronze
powder, cobalt powder, copper powder, iron powder, molybdenum
powder, nickel powder, stainless steel powder, titanium metal
powder, zirconium oxide powder, aluminum flakes, tungsten metal
powder, beryllium metal powder, zinc metal powder, or tin metal
powder. Examples of metal oxides include, but are not limited to,
zinc oxide, iron oxide, aluminum oxide, titanium dioxide, magnesium
oxide, zirconium oxide, and tungsten trioxide.
[0050] Outer Core Composition
[0051] As discussed above, the inner core (center) may be formed
from metal-containing thermoset or thermoplastic compositions and
is formed preferably from a metal-filled thermoset rubber.
Likewise, the outer core layer may be formed from thermoset or
thermoplastic materials. In one particularly preferred embodiment,
the outer core layer is formed from a thermoplastic composition.
Thus, in one preferred version, the inner core is formed from a
metal-containing thermoset composition and the outer core is formed
from a thermoplastic composition. In another version, the inner and
outer core layers are formed from thermoplastic compositions. More
particularly, the inner core is formed from a first
metal-containing thermoplastic composition and the outer core layer
is formed from a second thermoplastic composition. The same or
different ingredients may be used to form the first and second
thermoplastic compositions, respectively. Suitable thermoplastic
materials that can be used to make the inner and outer core layers
are described further below.
[0052] Preferably, an ionomer composition comprising an ethylene
acid copolymer containing acid groups that are at least partially
neutralized is used to form the thermoplastic composition. In one
embodiment, the neutralization level is greater than 70%. For
example, the neutralization level may be at least 90%, and even at
least 100% in some instances. Alternatively, the neutralization
level may be less than 70%.
[0053] Suitable ethylene acid copolymers that may be used to form
the respective compositions of this invention are generally
referred to as copolymers of ethylene; C.sub.3 to C.sub.8 .alpha.,
.beta.-ethylenically unsaturated mono-or dicarboxylic acid; and
optional softening monomer. Copolymers may 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.
[0054] When a softening monomer is included, such copolymers are
referred to herein as E/X/Y-type copolymers, wherein E is ethylene;
X is a C.sub.3 to C.sub.8 .alpha., .beta.-ethylenically unsaturated
mono- or dicarboxylic acid; and Y is a softening monomer. The
softening monomer is typically an alkyl (meth) acrylate, wherein
the alkyl groups have from 1 to 8 carbon atoms. 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.
[0055] 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.
[0056] The acidic groups in the copolymeric ionomers are partially
or totally neutralized with a cation source. Suitable cation
sources include metal cations and salts thereof, organic amine
compounds, ammonium, and combinations thereof. Preferred cation
sources are metal cations and salts thereof, wherein the metal is
preferably lithium, sodium, potassium, magnesium, calcium, barium,
lead, tin, zinc, aluminum, manganese, nickel, chromium, copper, or
a combination thereof. The metal cation salts provide the cations
capable of neutralizing (at varying levels) the carboxylic acids of
the ethylene acid copolymer and fatty acids, if present, as
discussed further below. These include, for example, the sulfate,
carbonate, acetate, oxide, or hydroxide salts of lithium, sodium,
potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum,
manganese, nickel, chromium, copper, or a combination thereof.
Preferred metal cation salts are calcium and magnesium-based salts.
High surface area cation particles such as micro and nano-scale
cation particles are preferred. The amount of cation used in the
composition is readily determined based on desired level of
neutralization.
[0057] For example, ionomeric resins having acid groups that are
neutralized from about 10 percent to about 100 percent may be used.
In one ionomer composition, the acid groups are partially
neutralized. That is, the neutralization level is from about 10% to
about 70%, more preferably 20% to 60%, and most preferably 30 to
50%. These ionomer compositions, containing acid groups neutralized
to 70% or less, may be referred to ionomers having relatively low
neutralization levels.
[0058] On the other hand, the ionomer composition may contain acid
groups that are highly or fully-neutralized. These highly
neutralized polymers (HNPs) are preferred for forming at least one
core layer in the present invention. In these HNPs, the
neutralization level is greater than 70%, preferably at least 90%
and even more preferably at least 100%. In another 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 one
preferred embodiment, a high acid ethylene acid copolymer
containing about 19 to 20 wt. % methacrylic or acrylic acid is
neutralized with zinc and sodium cations to a 95% neutralization
level.
[0059] "Ionic plasticizers" such as organic acids or salts of
organic acids, particularly fatty acids, may be added to the
ionomer resin if needed. 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 one preferred
embodiment, the thermoplastic ionomer composition, containing acid
groups neutralized to 70% or less, does not include a fatty acid or
salt thereof, or any other ionic plasticizer. On the other hand,
the thermoplastic ionomer composition, containing acid groups
neutralized to greater than 70%, includes an ionic plasticizer,
particularly a fatty acid or salt thereof. For example, the ionic
plasticizer may be added in an amount of 0.5 to 10 pph, more
preferably 1 to 5 pph. 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).
[0060] As noted above, the final ionomer compositions may contain
additional materials such as, for example, a small amount of ionic
plasticizer, which is particularly effective at improving the
processability of highly-neutralized ionomers. For example, the
ionic plasticizer may be added in an amount of 0.5 to 10 pph, more
preferably 1 to 5 pph. In addition to the fatty acids and salts of
fatty acids discussed above, other suitable ionic plasticizers
include, for example, polyethylene glycols, waxes, bis-stearamides,
minerals, and phthalates. In another embodiment, an amine or
pyridine compound is used, preferably in addition to a metal
cation. Suitable examples include, for example, ethylamine,
methylamine, diethylamine, tert-butylamine, dodecylamine, and the
like.
[0061] The ionomer compositions may contain a wide variety of
fillers and some of these fillers may be used to adjust the
specific gravity of the composition as needed. High surface-area
fillers that have an affinity for the acid groups in ionomer may be
used. In particular, fillers such as particulate, fibers, or flakes
having cationic nature such that they may also contribute to the
neutralization of the ionomer are suitable. 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 may be used.
Also, silica, fumed silica, and precipitated silica, such as those
sold under the tradename, HISIL.TM. from PPG Industries, carbon
black, carbon fibers, and nano-scale materials such as nanotubes,
nanoflakes, nanofillers, and nanoclays may be used. Other additives
and fillers include, but are not limited to, chemical blowing and
foaming agents, optical brighteners, coloring agents, fluorescent
agents, whitening agents, UV absorbers, light stabilizers,
defoaming agents, processing aids, antioxidants, stabilizers,
softening agents, fragrance components, plasticizers, impact
modifiers, titanium dioxide, acid copolymer wax, surfactants,
rubber regrind (recycled core material), clay, mica, talc, glass
flakes, milled glass, and mixtures thereof. Suitable additives are
more fully described in, for example, Rajagopalan et al., U.S.
Patent Application Publication No. 2003/0225197, the entire
disclosure of which is hereby incorporated herein by reference. In
a particular embodiment, the total amount of additive(s) and
filler(s) present in the final thermoplastic ionomeric composition
is 15 wt % or less, or 12 wt % or less, or 10 wt % or less, or 9 wt
% or less, or 6 wt % or less, or 5 wt % or less, or 4 wt % or less,
or 3 wt % or less, based on the total weight of the ionomeric
composition.
[0062] The ethylene acid copolymer 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 ethylene acid
copolymer is about 40 to about 95 weight percent. Other suitable
thermoplastic polymers that may be used to form the inner and outer
core layers include, but are not limited to, the following polymers
(including homopolymers, copolymers, and derivatives thereof):
[0063] (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;
[0064] (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;
[0065] (c) polyurethanes, polyureas, polyurethane-polyurea hybrids,
and blends of two or more thereof;
[0066] (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;
[0067] (e) polystyrenes, such as poly(styrene-co-maleic anhydride),
acrylonitrile-butadiene-styrene, poly(styrene sulfonate),
polyethylene styrene, and blends of two or more thereof;
[0068] (f) polyvinyl chlorides and grafted polyvinyl chlorides, and
blends of two or more thereof;
[0069] (g) polycarbonates, blends of
polycarbonate/acrylonitrile-butadiene-styrene, blends of
polycarbonate/polyurethane, blends of polycarbonate/polyester, and
blends of two or more thereof;
[0070] (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;
[0071] (i) polyimides, polyetherketones, polyamideimides, and
blends of two or more thereof; and
[0072] (j) polycarbonate/polyester copolymers and blends.
[0073] These thermoplastic polymers may be used by and in
themselves to form the inner and outer core layers, or blends of
thermoplastic polymers including the above-described polymers and
ethylene acid copolymer ionomers may be used. It also is recognized
that the ionomer compositions may contain a blend of two or more
ionomers. For example, the composition may contain a 50/50 wt. %
blend of two different highly-neutralized ethylene/methacrylic acid
copolymers. In another version, the composition may contain a blend
of one or more ionomers and a maleic anhydride-grafted
non-ionomeric polymer. The non-ionomeric polymer may be a
metallocene-catalyzed polymer. In another version, the composition
contains a blend of a highly-neutralized ethylene/methacrylic acid
copolymer and a maleic anhydride-grafted metallocene-catalyzed
polyethylene. In yet another version, the composition contains a
material selected from the group consisting of highly-neutralized
ionomers optionally blended with a maleic anhydride-grafted
non-ionomeric polymer; polyester elastomers; polyamide elastomers;
and combinations of two or more thereof.
[0074] More particularly, in one version, the same thermoplastic
composition used to form the inner core also may be used to form
the outer core layer. Alternatively, in other versions, different
thermoplastic compositions are used to form the inner and outer
core layers. For example, in one embodiment, the inner and outer
core layers have the same specific gravity levels. In a second
embodiment, the specific gravity of the inner core is greater than
the specific gravity of the outer core layer. Finally, in a third
embodiment, the specific gravity of the inner core is less than the
specific gravity of the outer core layer. Thus, both the inner and
outer core layers may be formed from an ethylene acid copolymer
ionomer composition, for example. The respective ethylene acid
copolymer compositions may contain metals as described above.
Conventional additives, for example, those additives described
below as being suitable for rubber formulations, also may be
included in the thermoplastic composition. The amount and type of
specific gravity fillers used in each layer, if any, may be
adjusted to achieve a desired specific gravity. For example, if the
objective is to make the specific gravities of the inner and outer
core layers different, in one example, the inner core layer may
contain a relatively small concentration of metal fillers, while
the outer core layer may contain a large concentration of metal
fillers. In another embodiment, the inner core and/or outer core
layer may not contain any metal materials. In yet another example,
the outer core layer may contain a small concentration of metal
fillers, while the inner core layer contains a large concentration
of metal materials. On the other hand, if the objective is to make
the specific gravities of the inner and outer core layers
substantially the same, then the inner and outer core layers may
contain the same concentration of metal fillers in the same
polymeric matrix.
[0075] As discussed above, the specific gravity of inner core layer
(SG.sub.inner) is preferably greater than the specific gravity of
the outer core layer (SG.sub.outer). In general, the specific
gravities of the respective pieces of an object affect the Moment
of Inertia (MOI) of the object. In general, the Moment of Inertia
of a ball (or other object) about a given axis 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 has a higher specific gravity than the outer piece),
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. Conversely, if the ball's mass is concentrated towards
the outer surface (the outer piece has a higher specific gravity
than the center piece), 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.
[0076] The golf balls of this invention having the above-described
core constructions show both good resiliency and spin control. The
resulting ball has a relatively high Coefficient of Restitution
(COR) allowing it to reach a high velocity when struck by a golf
club. Thus, the ball tends to travel a long distance and this is
particularly important for driver shots off the tee. At the same
time, the ball has a soft touch and feel. Thus, the golfer has
better control over the ball which is particularly important when
making approach shots using irons near the green. The golfer can
hit the ball with a soft touch so that it drops and stops quickly
on the green. Furthermore, professional and highly skilled
recreational golfers can place a back-spin on the ball for even
better accuracy and shot-control. For such golfers, the right
amount of spin and touch can be placed on the ball easily. The ball
is more playable and the golfer has more comfort playing with such
a ball. The golfer can hit the ball so that it flies the correct
distance while maintaining control over flight trajectory, spin,
and placement.
[0077] 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.
The specific gravity may be measured according to ASTM test
specification ASTM D-792-98. In addition, the cores of this
invention typically have a COR of about 0.75 or greater; and
preferably about 0.80 or greater. The compression of the core
preferably is about 50 to about 130 and more preferably in the
range of about 70 to about 110.
[0078] Curing of Rubber Composition
[0079] The rubber compositions of this invention 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.
[0080] 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.
[0081] 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.
[0082] As discussed above, the compositions of this invention are
formulated to have specific gravity levels so that they can be used
to form certain core components of the golf ball. In addition to
the metal fillers discussed above, the rubber compositions may
contain other additives. Examples of useful fillers include but are
not limited to, carbonaceous materials such as graphite and carbon
black. graphite fibers, precipitated hydrated silica, clay, talc,
glass fibers, aramid fibers, mica, calcium metasilicate, barium
sulfate, zinc sulfide, silicates, diatomaceous earth, calcium
carbonate, magnesium carbonate, rubber regrind (which is recycled
uncured rubber material which is mixed and ground), cotton flock,
natural bitumen, cellulose flock, and leather fiber. Micro balloon
fillers such as glass and ceramic, and fly ash fillers can also be
used.
[0083] In a particular aspect of this embodiment, the rubber
composition includes filler(s) selected from carbon black,
nanoclays (e.g., 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.), 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.
[0084] In addition, the rubber compositions may include
antioxidants to prevent the breakdown of the elastomers. 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.)
[0085] 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, antioxidants, antiozonants, as
well as other additives known in the art may be added to the rubber
composition.
[0086] Cover Structure
[0087] The golf ball cores of this invention may be enclosed with
one or more cover layers. In one 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 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.
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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.
[0092] 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 above-described ionomer
resins preferably would be used as the outer cover material.
[0093] Golf Ball Construction
[0094] The solid cores for the golf balls of this invention may be
made using any suitable conventional technique such as, for
example, compression or injection molding. Typically, the inner
core is formed by compression molding a slug of the uncured or
lightly cured polybutadiene rubber material into a spherical
structure. The outer core, which surrounds the inner core, is
formed by molding a composition over the inner core. Compression or
injection molding techniques may be used. Then, the intermediate
and/or cover layers are applied. 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.
[0095] The cover layers are formed over the core or ball
subassembly (the core structure and any intermediate 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 ball subassembly in
a compression mold. Under sufficient heating and pressure, the
shells fuse together to form an inner cover layer that surrounds
the subassembly. In another method, the ionomer composition is
injection-molded directly onto the core using retractable pin
injection molding. An outer cover layer comprising a polyurethane
or polyurea composition may be formed by using a casting
process.
[0096] For example, in one version of the casting process, a liquid
mixture of reactive polyurethane prepolymer and chain-extender
(curing agent) is poured into lower and upper mold cavities. Then,
the golf ball subassembly is lowered at a controlled speed into the
reactive mixture. Ball suction cups can hold the ball subassembly
in place via reduced pressure or partial vacuum. After sufficient
gelling of the reactive mixture (typically about 4 to about 12
seconds), the vacuum is removed and the intermediate ball is
released into the mold cavity. Then, the upper mold cavity is mated
with the lower mold cavity under sufficient pressure and heat. An
exothermic reaction occurs when the polyurethane prepolymer and
chain extender are mixed and this continues until the cover
material encapsulates and solidifies around the ball subassembly.
Finally, the molded balls are cooled in the mold and removed when
the molded cover is hard enough so that it can be handled without
deformation.
[0097] 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.
[0098] 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.
[0099] Different ball constructions can be made using the core
construction of this invention as shown in FIGS. 1 and 2 discussed
above. Such golf ball designs include, for example, three-piece,
four-piece, and five-piece designs. It should be understood that
the golf balls shown in FIGS. 1 and 2 are for illustrative purposes
only and are not meant to be restrictive. Other golf ball
constructions can be made in accordance with this invention.
[0100] Test Methods
[0101] 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.
[0102] 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 subassembly 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.
[0103] 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.
[0104] 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.
[0105] 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.
[0106] 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 Atti compression and is measured
according to a known procedure, using an Atti compression test
device, wherein a piston is used to compress a ball against a
spring. The travel of the piston is fixed and the deflection of the
spring is measured. The measurement of the deflection of the spring
does not begin with its contact with the ball; rather, there is an
offset of approximately the first 1.25 mm (0.05 inches) of the
spring's deflection. Very low stiffness cores will not cause the
spring to deflect by more than 1.25 mm and therefore have a zero
compression measurement. The Atti compression tester is designed to
measure objects having a diameter of 42.7 mm (1.68 inches); thus,
smaller objects, such as golf ball cores, must be shimmed to a
total height of 42.7 mm to obtain an accurate reading. Conversion
from Atti compression to Riehle (cores), Riehle (balls), 100 kg
deflection, 130-10 kg deflection or effective modulus can be
carried out according to the formulas given in J. Dalton.
Compression may be measured as described in McNamara et al., U.S.
Pat. No. 7,777,871, the disclosure of which is hereby incorporated
by reference.
[0107] Coefficient of Restitution ("COR"). The COR is determined
according to a known procedure, wherein a golf ball or golf ball
subassembly (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).
[0108] When numerical lower limits and numerical upper limits are
set forth herein, it is contemplated that any combination of these
values may be used. Other than in the operating examples, or unless
otherwise expressly specified, all of the numerical ranges,
amounts, values and percentages such as those for amounts of
materials and others in the specification may be read as if
prefaced by the word "about" even though the term "about" may not
expressly appear with the value, amount or range. Accordingly,
unless indicated to the contrary, the numerical parameters set
forth in the specification and attached claims are approximations
that may vary depending upon the desired properties sought to be
obtained by the present invention.
[0109] All patents, publications, test procedures, and other
references cited herein, including priority documents, are fully
incorporated by reference to the extent such disclosure is not
inconsistent with this invention and for all jurisdictions in which
such incorporation is permitted.
[0110] It is understood that the compositions and golf ball
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 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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