U.S. patent application number 12/560654 was filed with the patent office on 2011-03-17 for method of post-mold crosslinking thermoplastic polyurethane golf ball cover compositions.
This patent application is currently assigned to NIKE, INC.. Invention is credited to David Goodwin.
Application Number | 20110064883 12/560654 |
Document ID | / |
Family ID | 43048965 |
Filed Date | 2011-03-17 |
United States Patent
Application |
20110064883 |
Kind Code |
A1 |
Goodwin; David |
March 17, 2011 |
Method Of Post-Mold Crosslinking Thermoplastic Polyurethane Golf
Ball Cover Compositions
Abstract
A golf ball includes a cover material containing a thermoplastic
polyurethane composition which may be crosslinked post-mold by
applying a radiation source such as ultraviolet light. The
thermoplastic polyurethane composition may be crosslinked under
controlled conditions selected to yield golf balls exhibiting
desired physical properties and performance characteristics, such
as hardness, spin, feel, and distance. In some examples, the golf
ball contains one or more additional components, such as a UV
curable topcoat, that may be simultaneously treated by the
radiation source, thus improving processing efficiency.
Inventors: |
Goodwin; David; (Portland,
OR) |
Assignee: |
NIKE, INC.
Beaverton
OR
|
Family ID: |
43048965 |
Appl. No.: |
12/560654 |
Filed: |
September 16, 2009 |
Current U.S.
Class: |
427/508 ;
427/487 |
Current CPC
Class: |
B29D 99/0042 20130101;
A63B 45/00 20130101; A63B 37/0039 20130101; B29L 2031/54 20130101;
A63B 37/0003 20130101; B29C 71/04 20130101; A63B 37/0076
20130101 |
Class at
Publication: |
427/508 ;
427/487 |
International
Class: |
C08F 2/48 20060101
C08F002/48; C08J 7/18 20060101 C08J007/18 |
Claims
1. A method of preparing a multi-piece golf ball comprising:
providing a core layer; providing a cover layer, wherein the cover
layer comprises at least one crosslinkable thermoplastic
polyurethane; molding the cover layer and core layer to form a golf
ball preform in a mold; removing the golf ball preform from the
mold; and irradiating the golf ball preform with an energy source
under conditions sufficient to crosslink the crosslinkable
thermoplastic polyurethane.
2. The method of claim 1 further comprising applying at least one
intermediate layer between the core layer and the cover layer.
3. The method of claim 2 wherein the at least one intermediate
layer comprises one or more dynamically vulcanized thermoplastic
elastomers, functionalized styrene-butadiene elastomers,
thermoplastic rubbers, thermoset elastomers, thermoplastic
urethanes, metallocene polymers, thermoset urethanes, ionomer
resins, or blends thereof.
4. The method of claim 1 wherein the cover layer further comprises
a material selected from the group consisting of ionomer,
thermoplastic, elastomer, urethane, balata, polybutadiene, and
combinations thereof.
5. The method of claim 1 wherein the core layer is formed from a
base composition comprising polybutadiene and about 20 to 50 parts
of a metal salt diacrylate, dimethacrylate, or
monomethacrylate.
6. The method of claim 5 wherein the base composition further
comprises natural rubber, styrene butadiene, isoprene, or
combinations thereof.
7. The method of claim 1 wherein the energy source comprises
ultraviolet radiation.
8. The method of claim 7 wherein the cover layer further comprises
a UV initiator selected from the group consisting of
1-hydroxycyclohexylphenylketone,
2,2-dimethoxy-1,2-diphenylethan-1-one,
1-[4-(2-hydroxyethoxy)-phenyl]-2-methyl-1-propanone (HHPMP), and
bis(2,4,6-trimethylbenzoyl)-phenyl-phosphoneoxide (BTPPO).
9. A method of preparing a multi-piece golf ball comprising:
preparing a golf ball preform by molding a cover layer and a core
layer to form the golf ball preform in a mold, wherein the cover
layer comprises at least one crosslinkable thermoplastic
polyurethane; removing the golf ball preform from the mold; storing
the golf ball preform for at least one day; determining demand for
golf ball properties, performance characteristics, or both; and
irradiating the golf ball preform with an energy source under
conditions sufficient to crosslink the crosslinkable thermoplastic
polyurethane according to the determined golf ball properties,
performance characteristics, or both.
10. The method of claim 9 wherein the energy source comprises
ultraviolet radiation.
11. The method of claim 10 wherein the cover layer further
comprises a UV initiator selected from the group consisting of
1-hydroxycyclohexylphenylketone,
2,2-dimethoxy-1,2-diphenylethan-1-one,
1-[4-(2-hydroxyethoxy)-phenyl]-2-methyl-1-propanone (HHPMP), and
bis(2,4,6-trimethylbenzoyl)-phenyl-phosphoneoxide (BTPPO).
12. The method of claim 9 further comprising distributing the golf
ball preform to at least one of a regional supplier, a wholesaler,
a retailer, and an end user, prior to the step of irradiating.
13. The method of claim 9 further comprising applying indicia to
the irradiated golf ball according to the golf ball properties,
performance characteristics, or both.
14. A method of preparing a multi-piece golf ball comprising:
providing a core layer; providing a cover layer, wherein the cover
layer comprises at least one crosslinkable thermoplastic
polyurethane; molding the cover layer and core layer to form a golf
ball preform in a mold; removing the golf ball preform from the
mold; applying an ultraviolet curable topcoat composition to the
golf ball preform; and irradiating the golf ball preform with
ultraviolet radiation under conditions sufficient to crosslink the
crosslinkable thermoplastic polyurethane and cure the topcoat
composition.
15. The method of claim 14 further comprising applying at least one
intermediate layer between the core layer and the cover layer.
16. The method of claim 14 wherein the at least one intermediate
layer comprises one or more dynamically vulcanized thermoplastic
elastomers, functionalized styrene-butadiene elastomers,
thermoplastic rubbers, thermoset elastomers, thermoplastic
urethanes, metallocene polymers, thermoset urethanes, ionomer
resins, or blends thereof.
17. The method of claim 14 wherein the cover layer further
comprises a material selected from the group consisting of ionomer,
thermoplastic, elastomer, urethane, balata, polybutadiene, and
combinations thereof.
18. The method of claim 14 wherein the core layer is formed from a
base composition comprising polybutadiene and about 20 to 50 parts
of a metal salt diacrylate, dimethacrylate, or
monomethacrylate.
19. The method of claim 18 wherein the base composition further
comprises natural rubber, styrene butadiene, isoprene, or
combinations thereof.
20. The method of claim 14 wherein the cover layer further
comprises a UV initiator selected from the group consisting of
1-hydroxycyclohexylphenylketone,
2,2-dimethoxy-1,2-diphenylethan-1-one,
1-[4-(2-hydroxyethoxy)-phenyl]-2-methyl-1-propanone (HHPMP), and
bis(2,4,6-trimethylbenzoyl)-phenyl-phosphoneoxide (BTPPO).
Description
BACKGROUND
[0001] Golf balls generally have either a one-piece construction or
several layers including an outer cover surrounding a core. A wound
ball configuration typically has a vulcanized rubber thread wound
under tension around a solid or semi-solid core, which is then
enclosed in a single or multi-layer covering of tough, protective
material. Another type of ball, a one-piece ball, typically formed
from a solid mass of moldable resilient material which has been
cured to develop the necessary degree of hardness. One-piece molded
balls generally do not have an enclosing cover. Multi-piece (two or
more pieces) non-wound balls generally have a solid or liquid core
of one or more layers, and a cover having one or more layers formed
over the core.
[0002] Many multi-piece golf balls have a cover containing an
ionomer resin to impart toughness and cut resistance. Examples of
such ionomers include Surlyn.RTM., available from E.I. DuPont de
Nemours and Company, and Iotek.RTM., available from
Exxon-Mobil.
[0003] Polyurethanes also have been used in cover materials of
multi-piece golf balls.
[0004] Polyurethanes may be formed by mixing two primary
ingredients during processing, most commonly a polyisocyanate,
e.g., diphenylmethane diisocyanate monomer, toluene diisocyanate,
or their derivatives, and a polyol, e.g., a polyester- or polyether
polyol. An isocyanate that is reacted with a polyamine forms a
polyurea. The term "polyurethane" is often used to describe
polyurethane/polyurea systems. Polyurethanes may be thermoset,
e.g., having a crosslinked molecular structure, or thermoplastic,
e.g., having a linear molecular structure. A polyurethane becomes
irreversibly "set" when a polyurethane prepolymer is crosslinked
with a polyfunctional curing agent, such as a polyamine or polyol.
The prepolymer typically is made from polyether or polyester.
Crosslinking occurs between the isocyanate groups and the hydroxyl
end-groups of the polyol. The physical properties of thermoset
polyurethanes may be adjusted by the degree of crosslinking. For
example, tightly crosslinked polyurethanes are fairly rigid and
strong, whereas a lower level of crosslinking results in materials
that are flexible and resilient. Depending upon the processing
method, reaction rates may be quite fast, e.g., as in the case for
some reaction injection molding (RIM) systems, or in other cases
may be several hours or longer, e.g., as in several coating
systems.
SUMMARY
[0005] The following presents a general summary of aspects of the
invention in order to provide a basic understanding of the
invention and various features of it. This summary is not intended
to limit the scope of the invention in any way, but it simply
provides a general overview and context for the more detailed
description that follows.
[0006] Aspects of this invention are directed to methods of
preparing multi-piece golf balls. In one example, a multi-piece
golf ball is prepared by providing a core layer and a cover layer.
The cover layer includes a crosslinkable thermoplastic
polyurethane. The cover layer and core layer are molded into a golf
ball preform. Any suitable molding technique may be used such as
injection molding, compression molding, retractable pin injection
molding, vacuum forming, reaction injection molding, liquid
injection molding, flow coating, and the like. The golf ball
preform is removed from the mold. The golf ball preform is then
irradiated under conditions sufficient to crosslink the
crosslinkable thermoplastic polyurethane. In some embodiments, one
or more intermediate layers are present between the core layer and
the cover layer, and/or the core may have a multi-layer
construction and/or the core may have a multi-layer
construction.
[0007] In another aspect, a multi-piece golf ball is prepared by
molding a cover layer and a core layer to form a golf ball preform
in a mold. The cover layer includes a crosslinkable thermoplastic
polyurethane. The golf ball preform is removed from the mold and
stored for at least one day. Demand for particular golf ball
properties and/or performance characteristics are then determined
The golf ball preform is then irradiated to crosslink the
crosslinkable thermoplastic polyurethane to achieve the desired
golf ball properties and/or performance characteristics.
[0008] In yet another aspect, a multi-piece golf ball is prepared
by providing a core layer and a cover layer. The cover layer
includes a crosslinkable thermoplastic polyurethane. The cover
layer and core layer are molded into a golf ball preform, and
removed from the mold. An ultraviolet curable topcoat composition
is applied to the exterior surface of the golf ball preform. The
golf ball preform is then irradiated with ultraviolet radiation to
simultaneously crosslink the crosslinkable thermoplastic
polyurethane and cure the UV curable topcoat composition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] A more complete understanding of the present invention and
certain advantages thereof may be acquired by referring to the
following detailed description in consideration with the
accompanying drawings, in which:
[0010] FIGS. 1 and 1A schematically illustrate a cross-sectional
view of a multi-piece golf ball.
[0011] FIG. 2 is a process flow diagram illustrating one example of
post-mold UV irradiation of thermoplastic polyurethane golf ball
cover compositions.
[0012] FIG. 3 is a process flow diagram illustrating an example of
post-distribution UV irradiation of thermoplastic polyurethane golf
ball cover compositions.
[0013] FIG. 4 is a process flow diagram illustrating an example of
simultaneous post-mold UV irradiation of thermoplastic polyurethane
in a cover composition and a UV curable topcoat.
DETAILED DESCRIPTION
[0014] In the following description of various example structures,
reference is made to the accompanying drawings, which form a part
hereof, and in which are shown by way of illustration various
example golf ball structures. Additionally, it is to be understood
that other specific arrangements of parts and structures may be
utilized and structural and functional modifications may be made
without departing from the scope of the present invention. Also,
while terms such as "top," "bottom," "front," "back," "rear,"
"side," "underside," "overhead," and the like may be used in this
specification to describe various example features and elements of
the invention, these terms are used herein as a matter of
convenience, e.g., based on the example orientations shown in the
figures and/or the orientations in typical use. Nothing in this
specification should be construed as requiring a specific three
dimensional or spatial orientation of structures.
[0015] A. General Description of Golf Balls and Manufacturing
Systems and Methods
[0016] Golf balls may be of varied constructions, e.g., one-piece
balls, two-piece balls, three-piece balls (including wound balls),
four-piece balls, etc. The difference in play characteristics
resulting from these different types of constructions can be quite
significant. Generally, golf balls may be classified as solid or
wound balls. Solid balls that have a two-piece construction,
typically a cross-linked rubber core, e.g., polybutadiene rubber
cross-linked with zinc diacrylate and/or similar cross-linking
agents, encased by a blended cover, e.g., ionomer resins, are
popular with many average recreational golfers. The combination of
the core and cover materials provide a relatively "hard" ball that
is virtually indestructible by golfers and one that imparts a high
initial velocity to the ball, resulting in improved distance.
Because the materials of which the ball is formed are very rigid,
two-piece balls tend to have a hard "feel" when struck with a club.
Likewise, due to their hardness, these balls have a relatively low
spin rate off the driver, which also helps provide greater
distance.
[0017] Wound balls are generally constructed from a liquid or solid
center surrounded by tensioned elastomeric material and covered
with a durable cover material, e.g., ionomer resin, or a softer
cover material, e.g., balata or polyurethane. Wound balls are
generally thought of as performance golf balls and have good
resiliency, desirable spin characteristics, and feel when struck by
a golf club. However, wound balls are generally difficult to
manufacture as compared to solid golf balls.
[0018] More recently, three- and four-piece balls have gained
popularity, both as balls for average recreational golfers as well
as performance balls for professional and other elite level
players.
[0019] A variety of golf balls have been designed to provide
particular playing characteristics. These characteristics generally
include the initial velocity and spin of the golf ball, which can
be optimized for various types of players. For instance, certain
players prefer a ball that has a high spin rate in order to control
and stop the golf ball around the greens. Other players prefer a
ball that has a low spin rate and high resiliency to maximize
distance. Generally, a golf ball having a hard core and a soft
cover will have a high spin rate. Conversely, a golf ball having a
hard cover and a soft core will have a low spin rate. Golf balls
having a hard core and a hard cover generally have very high
resiliency for distance, but are hard feeling and difficult to
control around the greens.
[0020] The carry distance of some conventional two-piece balls has
been improved by altering the typical single layer core and single
cover layer construction to provide a multi-layer ball, e.g., a
dual cover layer, a dual core layer, and/or a ball having an
intermediate layer disposed between the cover and the core (also
called a "mantle" layer). Three- and four-piece balls (and even
five-piece balls) are now commonly found and commercially
available. Aspects of this invention may be applied to all types of
constructions, including the various wound, solid, and/or
multi-layer ball constructions with any number of layers described
above.
[0021] FIGS. 1 and 1A show an example of a golf ball 10, which has
a core 12, an intermediate layer 14, a cover 16 having a plurality
of dimples 18, and a topcoat 20 applied over the exterior surface
of the golf ball 10. The ball 10 also may have any other
construction, including the various example constructions described
herein. The thickness of the topcoat 20 typically is significantly
less than that of the cover 16 or the intermediate layer 14, and by
way of example may range from about 5 to about 25 .mu.m. The
topcoat 20 should have a minimal effect on the depth and volume of
the dimples 18.
[0022] The cover 16 of the golf ball 10 may be made of any number
of materials such as, but not limited to, ionomeric, thermoplastic,
elastomeric, urethane, balata (natural or synthetic),
polybutadiene, or combinations thereof As described below, at least
one layer of the cover 16 contains a crosslinkable thermoplastic
polyurethane. An optional primer or basecoat may be applied to the
exterior surface of the cover 16 of the golf ball 10 prior to
application of the coating layer 20.
[0023] The Center
[0024] A golf ball may be formed, for example, with a center having
a low compression, but still exhibit a finished ball COR and
initial velocity approaching that of conventional two-piece
distance balls. The center may have, for example, a compression of
about 60 or less. The finished balls made with such centers have a
COR, measured at an inbound speed of 125 ft./s., of about 0.795 to
about 0.815. "COR" refers to Coefficient of Restitution, which is
obtained by dividing a ball's rebound velocity by its initial
(i.e., incoming) velocity. This test is performed by firing the
samples out of an air cannon at a vertical steel plate over a range
of test velocities (e.g., from 75 to 150 ft/s). A golf ball having
a high COR dissipates a smaller fraction of its total energy when
colliding with the plate and rebounding therefrom than does a ball
with a lower COR.
[0025] The terms "points" and "compression points" refer to the
compression scale or the compression scale based on the ATTI
Engineering Compression Tester. This scale, which is well known to
persons skilled in the art, is used in determining the relative
compression of a center or ball.
[0026] The center may have, for example, a Shore D hardness of
about 65 to about 80. The center may have, for example, a diameter
of about 1.25 inches to about 1.5 inches. The base composition for
forming the center may include, for example, polybutadiene and
about 20 to 50 parts of a metal salt diacrylate, dimethacrylate, or
monomethacrylate. If desired, the polybutadiene can also be mixed
with other elastomers known in the art, such as natural rubber,
styrene butadiene, and/or isoprene, in order to further modify the
properties of the center. When a mixture of elastomers is used, the
amounts of other constituents in the center composition are usually
based on 100 parts by weight of the total elastomer mixture.
[0027] Metal salt diacrylates, dimethacrylates, and
monomethacrylates include without limitation those wherein the
metal is magnesium, calcium, zinc, aluminum, sodium, lithium or
nickel. Zinc diacrylate, for example, provides golf balls with a
high initial velocity in the United States Golf Association
("USGA") test.
[0028] Free radical initiators often are used to promote
cross-linking of the metal salt diacrylate, dimethacrylate, or
monomethacrylate and the polybutadiene. Suitable free radical
initiators include, but are not limited to peroxide compounds, such
as dicumyl peroxide; 1,1-di(t-butylperoxy) 3,3,5-trimethyl
cyclohexane; bis(t-butylperoxy)diisopropylbenzene; 2,5-dimethyl-2,5
di(t-butylperoxy)hexane; or di-t-butyl peroxide; and mixtures
thereof The initiator(s) at 100 percent activity may be added in an
amount ranging from about 0.05 to about 2.5 pph based upon 100
parts of butadiene rubber, or butadiene rubber mixed with one or
more other elastomers. Often the amount of initiator added ranges
from about 0.15 to about 2 pph, and more often from about 0.25 to
about 1.5 pph. The golf ball centers may incorporate 5 to 50 pph of
zinc oxide (ZnO) in a zinc diacrylate-peroxide cure system that
cross-links polybutadiene during the core molding process.
[0029] The center compositions may also include fillers, added to
the elastomeric composition to adjust the density and/or specific
gravity of the center. Non-limiting examples of fillers include
zinc oxide, barium sulfate, and regrind, e.g., recycled core
molding matrix ground to about 30 mesh particle size. The amount
and type of filler utilized is governed by the amount and weight of
other ingredients in the composition, bearing in mind a maximum
golf ball weight of 1.620 oz has been established by the USGA.
Fillers usually range in specific gravity from about 2.0 to about
5.6. The amount of filler in the center may be lower such that the
specific gravity of the center is decreased.
[0030] The specific gravity of the center may range, for example,
from about 0.9 to about 1.3, depending upon such factors as the
size of the center, cover, intermediate layer and finished ball, as
well as the specific gravity of the cover and intermediate
layer.
[0031] Other components such as accelerators, e.g., tetra
methylthiuram, processing aids, processing oils, plasticizers, dyes
and pigments, antioxidants, as well as other additives well known
to the skilled artisan may also be used in amounts sufficient to
achieve the purpose for which they are typically used.
[0032] Intermediate Layer(s)
[0033] The golf ball also may have one or more intermediate layers
formed, for example, from dynamically vulcanized thermoplastic
elastomers, functionalized styrene-butadiene elastomers,
thermoplastic rubbers, thermoset elastomers, thermoplastic
urethanes, TPEs, metallocene polymers, thermoset urethanes, ionomer
resins, or blends thereof For example, an intermediate layer may
include a thermoplastic or thermoset polyurethane. Non-limiting
examples of commercially available dynamically vulcanized
thermoplastic elastomers include SANTOPRENE.RTM., SARLINK.RTM.,
VYRAM.RTM., DYTRON.RTM., and VISTAFLEX.RTM.. SANTOPRENE.RTM. is a
dynamically vulcanized PP/EPDM. Examples of functionalized
styrene-butadiene elastomers, i.e., styrene-butadiene elastomers
with functional groups such as maleic anhydride or sulfonic acid,
include KRATON FG-1901x and FG-1921x, which are available from the
Shell Corporation of Houston, Tex.
[0034] Non-limiting examples of suitable thermoplastic
polyurethanes include ESTANE.RTM. 58133, ESTANE.RTM. 58134 and
ESTANE.RTM. 58144, which are commercially available from the
Lubrizol Company of Cleveland, Ohio.
[0035] Examples of metallocene polymers, i.e., polymers formed with
a metallocene catalyst, include those commercially available from
Sentinel Products of Hyannis, Mass. Suitable thermoplastic
polyesters include polybutylene terephthalate. Thermoplastic
ionomer resins may be obtained by providing a cross metallic bond
to polymers of monoolefin with at least one member selected from
the group consisting of unsaturated mono- or di-carboxylic acids
having 3 to 12 carbon atoms and esters thereof (the polymer
contains 1 to 50 percent by weight of the unsaturated mono- or
di-carboxylic acid and/or ester thereof). More particularly, low
modulus ionomers such as acid-containing ethylene copolymer
ionomers, include E/X/Y copolymers where E is ethylene, X is a
softening comonomer such as acrylate or methacrylate. Non-limiting
examples of ionomer resins include SURLYN.RTM. and LOTEK.RTM.,
which are commercially available from DuPont and Exxon-Mobil,
respectively.
[0036] Alternatively, the intermediate layer may be a blend of a
first and a second component wherein the first component is a
dynamically vulcanized thermoplastic elastomer, a functionalized
styrene-butadiene elastomer, a thermoplastic or thermoset
polyurethane or a metallocene polymer and the second component is a
material such as a thermoplastic or thermoset polyurethane, a
thermoplastic polyetherester or polyetheramide, a thermoplastic
ionomer resin, a thermoplastic polyester, another dynamically
vulcanized elastomer, another a functionalized styrene-butadiene
elastomer, another a metallocene polymer or blends thereof. At
least one of the first and second components may include a
thermoplastic or thermoset polyurethane.
[0037] An intermediate layer also may be formed from a blend
containing an ethylene methacrylic/acrylic acid copolymer.
Non-limiting examples of acid-containing ethylene copolymers
include ethylene/acrylic acid; ethylene/methacrylic acid;
ethylene/acrylic acid/n- or isobutyl acrylate; ethylene/methacrylic
acid/n- or iso-butyl acrylate; ethylene/acrylic acid/methyl
acrylate; ethylene/methacrylic acid/methyl acrylate;
ethylene/acrylic acid/iso-bornyl acrylate or methacrylate and
ethylene/methacrylic acid/isobornyl acrylate or methacrylate.
Examples of commercially available ethylene methacrylic/acrylic
acid copolymers include NUCREL.RTM. polymers, available from
DuPont.
[0038] Alternatively, an intermediate layer may be formed from a
blend which includes an ethylene methacrylic/acrylic acid copolymer
and a second component which includes a thermoplastic material.
Suitable thermoplastic materials for use in the intermediate blend
include, but are not limited to, polyesterester block copolymers,
polyetherester block copolymers, polyetheramide block copolymers,
ionomer resins, dynamically vulcanized thermoplastic elastomers,
styrene-butadiene elastomers with functional groups such as maleic
anhydride or sulfonic acid attached, thermoplastic polyurethanes,
thermoplastic polyesters, metallocene polymers, and/or blends
thereof
[0039] The intermediate layer often has a specific gravity of about
0.8 or more. In some examples the intermediate layer has a specific
gravity greater than 1.0, e.g., ranging from about 1.2 to about
1.3. Specific gravity of the intermediate layer may be adjusted,
for example, by adding a filler such as barium sulfate, zinc oxide,
titanium dioxide and combinations thereof.
[0040] The intermediate layer blend may have a flexural modulus of
less than about 10,000 psi, often from about 5,000 to about 8,000
psi. The intermediate layers often have a Shore D hardness of about
35 to 50. The intermediate layer and core construction together may
have a compression of less than about 65, often from about 50 to
about 65. Usually, the intermediate layer has a thickness from
about 0.020 inches to about 0.125 inches.
[0041] The golf balls may include a single intermediate layer or a
plurality of intermediate layers. In the case where a ball includes
a plurality of intermediate layers, a first intermediate layer may
include, for example, a thermoplastic material having a hardness
greater than that of the core. A second intermediate layer may be
disposed around the first intermediate layer and may have a greater
hardness than that of the first intermediate layer. The second
intermediate layer may be formed of, but not limited to, materials
such as polyether or polyester thermoplastic urethanes, thermoset
urethanes, and ionomers such as acid-containing ethylene copolymer
ionomers.
[0042] In addition, a third intermediate layer may be disposed in
between the first and second intermediate layers. The third
intermediate layer may be formed of the variety of materials as
discussed above. For example, the third intermediate layer may have
a hardness greater than that of the first intermediate layer. There
may also be additional intermediate layers.
[0043] The Cover Layer
[0044] A golf ball also typically has a cover layer that includes
one or more layers of a thermoplastic or thermosetting material. A
variety of materials may be used such as ionomer resins,
polyurethanes, balata and blends thereof. As described herein, at
least one of the layers in the cover layer includes a crosslinkable
thermoplastic polyurethane (TPU). The crosslinkable thermoplastic
polyurethane is initially a thermoplastic, and while in this state
may be melted and solidified repeatedly. Crosslinking generally
increases hardness and, as described more fully below, may be
controlled to impart desired properties to the cover and thus
performance characteristics to the golf ball.
[0045] Polyurethanes typically are formed by reacting a polyol with
a polyisocyanate. In some cases, the polyisocyanate is in the form
of a polyurethane prepolymer formed by reaction between a polyether
or polyester and a polyisocyanate. Two types of polyisocyanates are
predominantly used to make polyurethanes, diphenylmethane
diisocyanate monomer (MDI) and its derivatives, and toluene
diisocyanate (TDI) and its derivatives.
[0046] MDI is the most widely used polyisocyanate. Both rigid and
flexible foams, reaction injection moldings, elastomers, coatings,
and casting compounds are made from MDI. There are three basic
grades of MDI, polymeric MDI, pure MDI, and pure MDI derivatives.
Pure MDI, which is produced from polymeric MDI, is a
low-melting-temperature (about 100.degree. F.) solid. Its primary
use is in thermoplastic and cast elastomers. It also is used as an
additive for synthetic fibers to achieve high fiber tenacity and
elongation.
[0047] Pure MDI derivatives may be tailored to provide specific
processing and reaction characteristics. A major use for these
solvent-free liquids is in reaction injection molding (RIM), but
they also find application in integral skin moldings, semi-flexible
moldings, and cast elastomers. Toluene diisocyanate, TDI, is used
primarily to make flexible foam, and also is used in elastomers,
sealants, and coatings. TDI's generally are water-white liquids
which have much higher isocyanate (--NCO) content than MDI and
lower molecular weights. MDI and TDI also may be blended,
particularly for producing flexible molded foams. The free-flowing,
brown liquid blends usually have nearly as high isocyanate contents
as does TDI.
[0048] There are two main types of polyols used in polyurethanes
systems, polyesters and polyethers. Polyols are usually identified
by their functionality. Functionality pertains to the number of
reactive sites, which controls crosslinking. The more crosslinked
(higher functionality), the more rigid the polyurethane.
Functionality is controlled by the initiator used to manufacture
the polyol. Glycerine, for example, is commonly used to initiate
triol (3 functional) polyols. An oxide such as propylene oxide,
ethylene oxide, or a combination, is often added to the initiator
to extend the molecular chain and tailor final processing and
performance characteristics of the polyol. Triols often are used to
produce flexible foams, while diols commonly are used for
elastomers, coatings, and sealants. Tetrols typically are used for
rigid foams.
[0049] Polyether-based polyols have greater resistance to
hydrolysis. Polyether polyols may be modified, for example, by in
situ polymerization of acrylonitrile/styrene monomers. The
resulting graft polyols generally produce flexible foams with
improved load-bearing properties as well as greater tensile and
tear strengths. Depending on the backbone on which these vinyl
monomers are grafted, a wide range of performance characteristics
may be developed.
[0050] Polyester polyols generally yield polyurethanes with greater
strength properties, wear resistance, and thermal stability than
polyether polyurethanes, and they can absorb more energy. Polyester
polyols are typically classed by molecular weight. Low molecular
weight polyols (e.g., less than 1500) are used in coatings, casting
compounds, and rigid foams. Medium molecular weight polyols (e.g.,
1550 to 2500) are often used in elastomers. High molecular weight
polyols (e.g., greater than 2500) are typically used in flexible
foams.
[0051] Although conventional TPUs do not readily crosslink, TPUs
may be made crosslinkable by adjusting the chemistry and/or with
the addition of co-agents. See, e.g., Limerkens et al. U.S.
2009/0197000 A1, the disclosure of which is hereby incorporated by
reference in its entirety. Non-limiting examples of commercially
available crosslinkable TPUs include Elastollan.TM. 1100, which are
polyether-based thermoplastic polyurethanes available from BASF
that exhibit excellent low temperature properties and hydrolysis
resistance. These products can be injection and blow molded and
extruded. Some grades are suitable for injection molding. When
compounded with an appropriate co-agent, Elastollan.TM. may be
crosslinked using irradiation. Other commercially available TPUs,
such as Urepan.TM., may be used when combined with an appropriate
co-agent, such as Liquiflex.TM., a hydroxyl terminated
polybutadiene available from Petroflex.
[0052] In general, the thermoplastic polyurethane does not
crosslink during molding, but may be crosslinked subsequent to
molding by applying energy from a suitable source. Numerous ways
are known to induce crosslinking in a polymer by free radical
initiation, including peroxide initiation and irradiation. In some
examples the TPU is crosslinked by irradiation, such as by gamma
rays or ultraviolet (UV) irradiation. Other forms of particle
irradiation, such as electron beam also may be used. The type of
irradiation may be selected based on such factors as the
composition of the underlying layers. For example, certain types of
irradiation may degrade windings in a wound golf ball. On the other
hand, balls with a solid core would not be subject to the same
concerns. Some types of irradiation may tend to crosslink (and thus
harden) the core. An appropriate source of irradiation may be
selected depending upon whether such an effect is desired.
[0053] A photoinitiator typically is added to facilitate
crosslinking by light energy, e.g., UV radiation. Non-limiting
examples of UV initiators include ketones such as
1-hydroxycyclohexylphenylketone,
2,2-dimethoxy-1,2-diphenylethan-1-one,
1-[4-(2-hydroxyethoxy)-phenyl]-2-methyl-1-propanone (HHPMP), and
(bis)acylphosphine-oxides such as
bis(2,4,6-trimethylbenzoyl)-phenyl-phosphoneoxide (BTPPO). The
amount of photoinitiator typically ranges from about 0.1 to about 4
percent by weight of the composition, more usually from about 0.2
to about 2 percent by weight.
[0054] The cover may also contain other components in addition to
the crosslinkable thermoplastic polyurethane. For example, one or
more layers of the cover may be formed of a composition including
very low modulus ionomers (VLMIs). As used herein, the term "very
low modulus ionomers," refers to ionomer resins that further
include a softening comonomer X, commonly a (meth)acrylate ester,
present from about 10 weight percent to about 50 weight percent in
the polymer. VLMIs are copolymers of an .alpha.-olefin, such as
ethylene, a softening agent, such as n-butyl-acrylate or
iso-butyl-acrylate, and an .alpha.,.beta.-unsaturated carboxylic
acid, such as acrylic or methacrylic acid, where at least part of
the acid groups are neutralized by a magnesium cation or other
cation. Other examples of softening comonomers include n-butyl
methacrylate, methyl acrylate, and methyl methacrylate. Generally,
a VLMI has a flexural modulus from about 2,000 psi to about 10,000
psi. VLMIs are sometimes referred to as "soft" ionomers.
[0055] Ionomers, such as acid-containing ethylene copolymer
ionomers, include E/X/Y copolymers where E is ethylene, X is a
softening comonomer such as acrylate or methacrylate present in 0
to 50 weight percent of the polymer, and Y is acrylic or
methacrylic acid present in 5 to 35 (often 10 to 20) weight percent
of the polymer, wherein the acid moiety is neutralized 1 to 90
percent (usually at least 40 percent) to form an ionomer by a
cation such as lithium, sodium, potassium, magnesium, calcium,
barium, lead, tin, zinc or aluminum, or a combination of such
cations, lithium, sodium and zinc being the most preferred.
Specific acid-containing ethylene copolymers include
ethylene/acrylic acid, ethylene/methacrylic acid, ethylene/acrylic
acid/n-butyl acrylate, ethylene/methacrylic acid/n-butyl acrylate,
ethylene/methacrylic acid/iso-butyl acrylate, ethylene/acrylic
acid/iso-butyl acrylate, ethylene/methacrylic acid/n-butyl
methacrylate, ethylene/acrylic acid/methyl methacrylate,
ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic
acid/methyl acrylate, ethylene/methacrylic acid/methyl
methacrylate, and ethylene/acrylic acid/n-butyl methacrylate.
[0056] To aid in the processing of the cover stock, ionomer resins
may be blended in order to obtain a cover having desired
characteristics. For this reason, the cover may be formed from a
blend of two or more ionomer resins. The blend may include, for
example, a very soft material and a harder material. Ionomer resins
with different melt flow indexes are often employed to obtain the
desired characteristics of the cover stock. SURLYN.RTM. 8118, 7930
and 7940 have melt flow indices of about 1.4, 1.8, and 2.6 g/10
min., respectively. SURLYN.RTM. 8269 and SURLYN.RTM. 8265 each have
a melt flow index of about 0.9 g/10 min. A blend of ionomer resins
may be used to form a cover having a melt flow index, for example,
of from about 1 to about 3 g/10 min. The cover layer may have a
Shore D hardness, for example, ranging from about 45 to about
70.
[0057] As another example, a thermoset cast polyurethane may be
used. Thermoset cast polyurethanes are generally prepared using a
diisocyanate, such as 2,4-toluene diisocyanate (TDI),
methylenebis-(4-cyclohexyl isocyanate) (HMDI), or para-phenylene
diisocyanate ("PPDI") and a polyol which is cured with a polyamine,
such as methylenedianiline (MDA), or a trifunctional glycol, such
as trimethylol propane, or tetrafunctional glycol, such as
N,N,N',N'-tetrakis(2-hydroxpropyl)ethylenediamine. Other suitable
thermoset materials include, but are not limited to, thermoset
urethane ionomers and thermoset urethane epoxies. Other examples of
thermoset materials include polybutadiene, natural rubber,
polyisoprene, styrene-butadiene, and styrene-propylene-diene
rubber.
[0058] When the cover includes more than one layer, e.g., an inner
cover layer and an outer cover layer, various constructions and
materials are suitable. For example, an inner cover layer may
surround the intermediate layer with an outer cover layer disposed
thereon or an inner cover layer may surround a plurality of
intermediate layers. When using an inner and outer cover layer
construction, the outer cover layer material may be a thermoset
material that includes at least one of a castable reactive liquid
material and reaction products thereof, as described above, and may
have a hardness from about 30 Shore D to about 60 Shore D.
[0059] The inner cover layer may be formed from a wide variety of
hard (e.g., about 65 Shore D or greater), high flexural modulus
resilient materials, which are compatible with the other materials
used in the adjacent layers of the golf ball. The inner cover layer
material may have a flexural modulus of about 65,000 psi or
greater. Suitable inner cover layer materials include the hard,
high flexural modulus ionomer resins and blends thereof, which may
be obtained by providing a cross metallic bond to polymers of
monoolefin with at least one member selected from the group
consisting of unsaturated mono- or di-carboxylic acids having 3 to
12 carbon atoms and esters thereof (the polymer contains 1 to 50
percent by weight of the unsaturated mono- or di-carboxylic acid
and/or ester thereof). More particularly, such acid-containing
ethylene copolymer ionomer component includes E/X/Y copolymers
where E is ethylene, X is a softening comonomer such as acrylate or
methacrylate present in 0-50 weight percent of the polymer, and Y
is acrylic or methacrylic acid present in 5-35 weight percent of
the polymer, wherein the acid moiety is neutralized about 1-90
percent to form an ionomer by a cation such as lithium, sodium,
potassium, magnesium, calcium, barium, lead, tin, zinc, or
aluminum, or a combination of such cations. Specific examples of
acid-containing ethylene copolymers include ethylene/acrylic acid,
ethylene/methacrylic acid, ethylene/acrylic acid/n-butyl acrylate,
ethylene/methacrylic acid/n-butyl acrylate, ethylene/methacrylic
acid/iso-butyl acrylate, ethylene/acrylic acid/iso-butyl acrylate,
ethylene/methacrylic acid/n-butyl methacrylate, ethylene/acrylic
acid/methyl methacrylate, ethylene/acrylic acid/methyl acrylate,
ethylene/methacrylic acid/methyl acrylate, ethylene/methacrylic
acid/methyl methacrylate, and ethylene/acrylic acid/n-butyl
methacrylate.
[0060] Non-limiting examples of other suitable inner cover
materials that may be present include thermoplastic or thermoset
polyetheresters, polyetheramides, or polyesters, dynamically
vulcanized elastomers, functionalized styrene-butadiene elastomers,
metallocene polymers, polyamides such as nylons, acrylonitrile
butadiene-styrene copolymers (ABS), and blends thereof.
[0061] The crosslinkable TPU may be irradiated using any
appropriate energy source, such as commercially available UV
radiation sources. Because of the spherical shape of the golf ball,
it is desirable to use devices that are capable of applying UV
radiation to three dimensional surfaces. The level of radiation may
be selected in accordance with the desired end characteristics of
the cover. In general, higher levels of radiation and/or longer
exposure times result in a higher degree of crosslinking (e.g.,
increased hardness), while lower levels of radiation and/or shorter
exposure times result in a lower degree of crosslinking (e.g., less
hardness and more elasticity). Dosage levels may vary over a wide
range, but by way of example often may range up from about 1 to
about 14 Mrads, more usually from about 2 to about 12 Mrads. In
general, the amount of energy (and thus degree of crosslinking) may
be controlled by adjusting one or more of the bulb type, exposure
time, filtration, and exposure distance.
[0062] The composition of the cover layer and level of radiation
may be selected to give a desired hardness, for example a Shore D
hardness ranging from about 45 to about 75, often from about 50 to
about 70. In general, crosslinking typically results in increasing
Shore D hardness of the cover by 1-5 units as compared to the
hardness before crosslinking.
[0063] Topcoat
[0064] The outer surface of the golf ball typically is painted with
at least one clear or pigmented basecoat primer followed by at
least one application of a clear topcoat. The clear topcoat may
serve a variety of functions, such as protecting the cover
material, improving aerodynamics of ball flight, preventing
yellowing, and/or improving aesthetics of the ball.
[0065] One common topcoat utilizes a solvent borne two-component
polyurethane, which is applied to the exterior of a golf ball. This
topcoat formulation generally requires the use of a solvent that is
a significant source of volatile organic compounds (VOC), which
pose environmental and health concerns. Ultraviolet (UV) curable
coatings generally do not require solvents. As described in
co-pending and commonly owned U.S. patent application Ser. No.
12/470,820, the topcoat may be applied using a nitrogen- or
nitrogen-enriched air delivery system. This pending U.S. patent
application is entirely incorporated herein by reference.
[0066] Non-limiting examples of topcoats include thermoplastics,
thermoplastic elastomers such as polyurethanes, polyesters,
acrylics, low acid thermoplastic ionomers, e.g., containing up to
about 15% acid, and UV curable systems. Additional additives
optionally may be incorporated into the coating material, such as
flow additives, mar/slip additives, adhesion promoters, thickeners,
gloss reducers, flexibilizers, cross-linking additives,
isocyanates, or other agents for toughening or creating scratch
resistance, optical brighteners, UV absorbers, and the like. The
amount of such additives usually ranges from 0 to about 5 wt %,
often from 0 to about 1.5 wt %. The thickness of the topcoat
typically ranges from of about 5 to about 25 .mu.m, and in some
examples ranges from about 10 to about 15 .mu.m.
[0067] As described below, in some examples in which a UV curable
topcoat is applied, the crosslinkable TPU in the cover composition
and the UV curable topcoat may be simultaneously exposed to UV
radiation such that the TPU is crosslinked and the topcoat is cured
in a single step.
[0068] Manufacturing Process
[0069] Golf balls may be formed using a variety of techniques, such
as injection molding, compression molding, retractable pin
injection molding, vacuum forming, reaction injection molding,
liquid injection molding, flow coating, and the like. One common
technique for manufacturing golf balls is a laminate process. In
order to form multiple layers around the center, a laminate is
first formed. The laminate includes at least two layers and
sometimes includes three layers. The laminate may be formed by
mixing uncured core material to be used for each layer and calendar
rolling the material into thin sheets. Alternatively, the laminate
may be formed by mixing uncured intermediate layer material and
rolling the material into sheets. The laminate sheets may be
stacked together to form a laminate having three layers, using
calender rolling mills. Alternatively, the sheets may be formed by
extrusion.
[0070] A laminate also may be formed using an adhesive between each
layer of material. For example, an epoxy resin may be used as
adhesive. The adhesive should have good shear and tensile strength,
for example, a tensile strength over about 1500 psi. The adhesive
often has a Shore D hardness of less than about 60 when cured. The
adhesive layer applied to the sheets should be very thin, e.g.,
less than about 0.004 inches thick.
[0071] Preferably, each laminate sheet is formed to a thickness
that is slightly larger than the thickness of the layers in the
finished golf ball. Each of these thicknesses can be varied, but
all usually have a thickness of less than about 0.1 inches. The
sheets should have very uniform thicknesses.
[0072] The next step in the method is to form multiple layers
around the center. This may be accomplished by placing two
laminates between a top mold and a bottom mold. The laminates may
be formed to the cavities in the mold halves. The laminates then
may be cut into patterns that, when joined, form a laminated layer
around the center. For example, the laminates may be cut into
figure 8-shaped or barbell-like patterns, similar to a baseball or
a tennis ball cover. Other patterns may be used, such as curved
triangles, hemispherical cups, ovals, or other patterns that may be
joined together to form a laminated layer around the center. The
patterns may then be placed between molds and formed to the
cavities in the mold halves. A vacuum source often is used to form
the laminates to the mold cavities so that uniformity in layer
thickness is maintained.
[0073] After the laminates have been formed to the cavities, the
centers are then inserted between the laminates. The laminates are
then compression molded about the center under conditions of
temperature and pressure that are well known in the art. The mold
halves usually have vents to allow flowing of excess layer material
from the laminates during the compression molding process. As an
alternative to compression molding, the core and/or intermediate
layer(s) may be formed by injection molding or other suitable
technique.
[0074] The next step involves forming a cover around the golf ball
core. The core, including center and intermediate layers, may be
supported within a pair of cover mold-halves by a plurality of
retractable pins. The retractable pins may be actuated by
conventional means known to those of ordinary skill in the art.
[0075] After the mold halves are closed together with the pins
supporting the core, the cover material is injected into the mold
in a liquid state through a plurality of injection ports or gates,
such as edge gates or sub-gates. With edge gates, the resultant
golf balls are all interconnected and may be removed from the mold
halves together in a large matrix. Sub-gating automatically
separates the mold runner from the golf balls during the ejection
of the golf balls from mold halves.
[0076] The retractable pins may be retracted after a predetermined
amount of cover material has been injected into the mold halves to
substantially surround the core. The liquid cover material is
allowed to flow and substantially fill the cavity between the core
and the mold halves, while maintaining concentricity between the
core and the mold halves. The cover material is then allowed to
solidify around the core, and the golf balls are ejected from the
mold halves and subjected to finishing processes, including
topcoating, painting, and/or other finishing processes, including
processes in accordance with examples of this invention, as will be
described in more detail below.
[0077] B. Specific Examples of Invention
[0078] With reference to FIG. 2, golf balls having a crosslinkable
TPU in the cover layer may be molded according to techniques
previously described to form a golf ball preform, and then removed
from the mold. The golf ball preform may be stored for a period of
time if desired. The shelf life of the preform (uncrosslinked golf
ball) may vary depending on the compositions of the various layers,
processing conditions, and the like. In most cases, the
uncrosslinked golf balls may be stored up to about one year or more
without any adverse affects. In some cases, precautions should be
taken to minimize light and/or high temperature exposure during
storage. After the targeted characteristics for the golf balls are
identified, the golf balls may be subjected to an energy source,
such as UV irradiation as previously described, to achieve the
desired properties and performance characteristics for the golf
balls. Optionally, indicia may be applied to the golf balls at that
point, using known techniques, to identify the properties and
performance characteristics. For example, a corresponding model
designation may be affixed to the golf balls after the cover layer
is crosslinked.
[0079] Post-mold crosslinking of the TPU in the cover layer offers
a number of advantages. For example, as schematically illustrated
in FIG. 3, golf balls may be first molded at a central
manufacturing site and then distributed to regional suppliers,
wholesalers, or possibly even further down the distribution chain
such as to retailers or end users. The golf balls may be then
stored for period of time (e.g., at least one day, one week, one
month, 2-10 months, one year, or longer), until the demand for
particular performance characteristics (e.g., distance, spin,
hardness, etc.) for golf balls may be assessed for that region or
location. The supplier, wholesaler, retailer, end user etc. may
then irradiate the golf balls with an energy source, e.g., a
commercially available UV energy source as previously described,
under prescribed conditions to selectively crosslink the TPU to
achieve the desired properties and performance characteristics.
This provides the benefit of quickly adapting to changes in
preferences or demand for particular characteristics of golf
balls.
[0080] In some instances, the (uncrosslinked) golf ball preforms
may be shipped to a third party prior to the step of irradiating.
For example, a supplier, distributor, etc. may ship the preforms to
a third party who carries out the irradiating step. In some
examples, the golf ball preform may be packaged (e.g., in sleeves
of 2, 3, or 4 balls, and/or in boxes of 12, 15, 18, or 24 balls)
prior to irradiation. The golf ball preforms may be unpacked by a
downstream entity (e.g., regional seller, wholesaler, retailer,
ultimate customer, etc.), and then irradiated to get the properties
desired by the consumer. Optionally, the balls may be repackaged
after the irradiation step. Indicia may be applied to the golf
balls and/or packaging material according to properties imparted to
the golf balls by the irradiation step.
[0081] In another aspect, the irradiation may be used to
simultaneously treat one or more other components of the golf ball
in addition to the crosslinkable TPU in the cover layer. For
example, as schematically illustrated in FIG. 4, golf balls may be
prepared having a crosslinkable TPU in the cover layer and a UV
curable topcoat. Exposure of the golf balls to UV radiation under
appropriate conditions may affect crosslinking of the TPU in the
cover layer, as well as curing of the UV curable topcoat. Other
components of the golf ball, such as the core and/or intermediate
layer(s), may also contain materials which are affected by the
radiation source. For example, some materials used in the core may
be hardened when exposed to UV radiation.
[0082] While the invention has been described in detail in terms of
specific examples including presently preferred modes of carrying
out the invention, those skilled in the art will appreciate that
there are numerous variations and permutations of the above
described systems and methods. Thus, the spirit and scope of the
invention should be construed broadly as set forth in the appended
claims.
* * * * *