U.S. patent application number 09/877386 was filed with the patent office on 2002-02-07 for uv curable coating for golf balls.
This patent application is currently assigned to Lord Corporation. Invention is credited to Jin, Pei-Wen, Quarmby, Ian C..
Application Number | 20020016226 09/877386 |
Document ID | / |
Family ID | 22781903 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020016226 |
Kind Code |
A1 |
Jin, Pei-Wen ; et
al. |
February 7, 2002 |
UV curable coating for golf balls
Abstract
An UV curable coating for a golf ball or a similar game ball
that the UV curable coating is the reaction product of at least one
UV-reactive component, a polyfunctional aziridines, and a
photo-initiator. The UV curable coating is substantially free of
solvent, therefore, contains nearly 100% solids.
Inventors: |
Jin, Pei-Wen; (Cary, NC)
; Quarmby, Ian C.; (Apex, NC) |
Correspondence
Address: |
Miles B. Dearth
111 Lord Drive
PO Box 8012
Cary
NC
27512-8012
US
|
Assignee: |
Lord Corporation
|
Family ID: |
22781903 |
Appl. No.: |
09/877386 |
Filed: |
June 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60210186 |
Jun 8, 2000 |
|
|
|
Current U.S.
Class: |
473/378 |
Current CPC
Class: |
C09D 175/16 20130101;
A63B 37/12 20130101; A63B 37/00221 20200801; C08G 18/833 20130101;
A63B 37/0003 20130101; C09D 4/06 20130101; C08G 18/672 20130101;
C08G 18/672 20130101; C08G 18/42 20130101; C09D 4/06 20130101; C08F
290/147 20130101 |
Class at
Publication: |
473/378 |
International
Class: |
A63B 037/12 |
Claims
What is claimed is:
1. A high solids, low-solvent containing outer coating for a golf
ball, comprising a UV curable coating which contains (a) at least
one UV-reactive component, (b) a polyfunctional aziridine having
the formulaR--[X--N(CH.sub.2).sub.2].sub.min which R is an organic
aliphatic radical or a hydrogen atom, X is an alkylene group which
may contain an ester group, an ether group, an amide group or a
similar inert group, and m is a number of 2 to 4, and (c) a
photo-initiator.
2. The coating of claim 1 wherein said UV-reactive component
comprises a urethane acrylate oligomer (a) formed by reacting
diisocyanate with a hydroxyl group containing acrylate or
methacrylate and the product further reacted with polyol or (b)
reacting a hydroxyl group containing acrylate or methacrylate with
a lactone and reacting the product with an isocyanate.
3. A golf ball comprising a top coat covering formed from a
UV-curable coating comprising at least one UV curable acrylate
oligomer, a polyfunctional aziridine, and a photoinitiator.
4. A coated substrate comprising a polymer as substrate and coated
with a UV cured coating comprising (a) at least one UV-reactive
component, (b) a polyfunctional aziridine having the
formulaR--[X--N(CH.sub.2).sub.2].sub.- min which R is an organic
aliphatic radical or a hydrogen atom, X is an alkylene group which
may contain an ester group, an ether group, an amide group or a
similar inert group, and m is a number of 2 to 4, and (c) a
photo-initiator.
5. The coated substrate of claim 3 wherein said UV-reactive
component comprises a urethane acrylate oligomer (a) formed by
reacting diisocyanate with a hydroxyl group containing acrylate or
methacrylate and the product further reacted with polyol or (b)
reacting a hydroxyl group containing acrylate or methacrylate with
a lactone and reacting the product with an isocyanate.
6. The golf ball according to claim 1 wherein UV curable acrylate
oligomer has a viscosity within the range of 8,000 centipoise to
about 40,000 centipoise.
7. The golf ball according to claim 1 wherein the photoinitiator is
present in an amount of from 1 to 8 % by weight of the coating.
8. The golf ball according to claim 1 wherein the photoinitiator is
selected from the group consisting of a benzophenone, benzoin,
acetophenone, benzoin methyl ether, Michler's ketone, benzoin butyl
ether, xanthone, thioxanthone, propiophenone, fluorenone,
carbozole, diethyoxyacetophenone, 2-, 3- and 4-
methylacetophenones, 2-, 3-and 4- methoxyacetophenones, 2- and
3-chloroxanthones, 2-, and 3-chlorothioxanthones,
2-acetyl-4-methylphenyl acetate, 2,2'-dimethyoxy-2-phenyl
acetophenone, benzaldehyde, fluorene, anthraquinone,
triphenylamine, 3- and 4-allyl-acetophenone, p-diacetylbenzene,
3-chloro-2-nonylxanthone, 2-chlorobenzophenone,
4-methoxybenzophenone, 2,2',4,4'-tetrachlorobenzophenone,
2-chloro-4'-methylbenzophenone, 4-chloro-4'-methylbenzophenone,
3-methylbenzophenone, 4-tert-butyl-benzophenone, isobutyl ether,
benzoic acetate, benzil, benzilic acid, amino benzoate, methylene
blue, 2,2-diethoxyacetophenone, 9,10-phenanthrenequinone, 2-methyl
anthraquinone, 2-ethyl anthraquinone, 1-tert-butyl-anthraquinone,
1,4-naphthoquinone, isopropylthioxanthone, 2-chlorothioxanthone,
2-iso-propylthioxanthone, 2methylthioxanthone, 2-decylthioxanthone,
2-dodecyl-thioxanthone, 2-methyl-1-[4-(methyl
thio)phenyl)]-2-morpholinop- ropanone-1, and any combination
thereof.
9. A golf ball comprising a top coat covering substantially the
entire golf ball, the top coat formed from a UV-curable coating
comprising 30 to 80% by weight on weight of the coating, of at
least one UV reactive component, 10 to 60% by weight of a reactive
diluent, a polyfunctional aziridine in an amount ranging from 0.1
to 15% by weight of the UV-curable coating, and a photoinitiator in
an amount ranging from 0.5 to 15% by weight of the UV-curable
coating.
10. The coated substrate according to claim 3 wherein the UV
reactive component is an oligomer selected from the group
consisting of urethane acrylate, epoxy acrylate or polyether
acrylate, the polyfunctional aziridine is present in the coating in
an amount of from 0.5% to 8% per weight of the coating, and the
photoinitiator in an amount of approximately 1 part per weight of
the UV-curable coating.
11. The golf ball according to claim 6 wherein the UV reactive
component comprises a urethane acrylate oligomer at from 40% to 70%
by weight of the coating and a reactive diluent in an amount of
from 10 to 60 % by weight.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an ultraviolet (UV) curable
coating. In particular, though not exclusively, the present
invention relates to a high solids UV curable coating useful in a
golf ball application.
BACKGROUND OF THE INVENTION
[0002] Golf balls can be classified as one-piece, two-piece, and
three-piece balls. One-piece balls are molded from a homogeneous
mass of material with a dimple pattern molded therein. Two-piece
balls are comprised of a cover molded over a solid core. The core
of a two-piece ball is typically formed of rubber and can be solid,
semi-solid or have a liquid center. Three-piece balls,
traditionally, include a rubber inner core, elastic wrappings and a
balata or SURLYN.RTM. ionomer cover. The more recent trend in the
golf ball art is towards the development of multi-component golf
balls such as balls having two or more cover layers, two or more
core layers or both multiple core and multiple cover layers.
[0003] Golf ball covers are presently formed from a variety of
materials, such as balata, SURLYN.RTM. ionomer resin, IOTEK.RTM.
resin and polyurethane, depending upon the performance
characteristics desired for the golf ball. One of the softest
materials conventionally used to form golf ball covers is balata,
which is the trans form of the 1,4-chain polymer of isoprene. For
many years, balata was the standard cover stock material used in
forming most golf balls. Balata covered balls are favored among
professionals and more advanced amateur players because the
softness of the cover allows the player to achieve spin rates
sufficient to precisely control ball direction and distance,
particularly on shorter approach shots.
[0004] However, because of its softness, balata is susceptible to
cuts or other damage to the cover resulting from a "mis-hit" shot.
Accordingly, harder, more durable cover materials, e.g.,
SURLYN.RTM. ionomer resin, have been developed which provide higher
durability, but less spin and feel, than the balata balls.
SURLYN.RTM. resins are generally ionic copolymers of an olefin such
as ethylene and a metal salt of an unsaturated carboxylic acid such
as acrylic acid, methacrylic acid or maleic acid. Metal ions, such
as lithium, zinc or sodium are used to neutralize some portion of
the acidic groups in the copolymer resulting in a thermoplastic
elastomer for use as a golf ball cover.
[0005] Additionally, various softening comonomers such as n-butyl
acrylate may be added during the ionomer manufacturing process to
improve golf ball performance characteristics such as spin and
feel. In the early 1980s, low modulus SURLYN.RTM. resin were
introduced and subsequently utilized to impart more spin and an
improved, balata-like feel to golf balls.
[0006] Primer coat and topcoat layers are commonly applied to the
golf ball cover to provide a high gloss and an overall enhanced
appearance to the ball. Solvent-borne coatings are currently used
as topcoats for golf balls or similar game balls. These coatings
provide good adhesion to the surface of the balls, and good
abrasion resistance. However, the solvent type systems have serious
environmental pollution problems, and the disadvantage of long cure
times, or high curing temperatures. U.S. Pat. No. 4,871,589
(hereinafter '589 patent) discloses a method of treating golf balls
by applying solvent-borne coating onto a thermoplastic ionomer
covered golf ball. The solvent-borne coating of '589 patent
contains 50% solvents and needs to be cured for 10 minutes at
50.degree. C.
[0007] In light of the increasing regulation of volatile organic
compounds (VOC), the use of traditional solvent-borne adhesive is
becoming problematic. To eliminate the problems posed by solvents,
water-borne replacements have been developed. Current water-borne
coatings suffer from drawback of long curing time. U.S. Pat. No.
4,459,326 discloses a water-based composition for coating synthetic
plastic surfaces. The water-based coating need to dry for 1/2 to 4
hours.
[0008] U.S. Pat. No 4,278,578 (hereinafter '578 patent) teaches an
aqueous coating containing polyfunctional aziridines. The '578
patent indicates that the use of more than 3% aziridine is not
beneficial to coating properties.
[0009] U.S. Pat. No. 5,300,325 discloses a use of an aziridine in a
water-borne primer to promote adhesion between the solvent-borne
topcoat and the cover of a golf ball. The primer and topcoat are
co-cured and crosslinked at 54.degree. C. for six hours.
[0010] U.S. Pat. No. 6,146,288 discloses a UV-curable coating and
method for coating golf balls and other substrates with a material
that includes one or more low viscosity polyether acrylates, a
functional carbodiimide resin, one or more low viscosity aliphatic
urethane polyacrylate oligomer, and a photoinitiator selected from
one or more of S mono-aryl ketones, trimethylbenzoyldiphenyl
phosphinates, and/or phosphine oxides. In addition, a method of
curing a UV-curable coating is disclosed. The method includes the
steps of spraying the formulation onto the exterior of a substrate,
surrounding the substrate in an inert gas environment, and
irradiating the substrate with ultraviolet radiation from a doped
medium pressure mercury vapor lamp.
[0011] SURLYN.RTM. resin is the most widely used material to make
golf ball cover layers. SURLYN.RTM. resin is an ionomer from the
copolymer of ethylene and methacrylic acid. It is difficult for an
UV curable coating to adhere to SURLYN.RTM. surface, in part
because of the high shrinkage during the polymerization process.
Urethane cured coatings are not easily adhered to ionomers. The
present invention resulted from solving an adhesion problem of a UV
curable coating which can be effectively utilized in coating
ionomer substrates.
[0012] The problem addressed by the present invention was to
provide an UV curable coating which would be capable of developing
excellent adhesion, even on substrates which are traditionally
difficult to adhere to with a UV coating. In addition, the UV
curable coating of the present invention provides a high gloss
finish, does not require the golf ball to be surrounded by an inert
gas, is low in yellowing, and also offers good stain resistance and
durability.
SUMMARY OF THE INVENTION
[0013] The present invention relates to an UV curable coating
comprising (a) at least one UV-reactive component, (b) a
polyfunctional aziridine, and (c) a photo-initiator. The UV curable
coating of this invention is substantially free of solvents, and
therefore, provides a nearly 100% solid system. The UV curable
coating of the present invention is particularly suitable for
coating ionomer substrates. Unexpectedly, the UV curable coating of
the invention shows improved whiteness index (WI) compared to
typical UV coatings. Specifically, the present invention discloses
a high solids UV curable coating for golf balls or a similar game
ball application.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] The UV curable coating of this invention comprises the
reaction product of (a) at least one UV-reactive component, (b) a
polyfunctional aziridines, and (c) a photo-initiator.
[0015] Polyfunctional aziridines ("polyaziridine") suitable for the
purposes of the present invention correspond to the formula:
R--[X--N(CH.sub.2).sub.2].sub.m
[0016] in which R is an organic aliphatic radical or a hydrogen
atom, X is an alkylene group which may contain an ester group, an
ether group, an amide group or a similar inert group, and m is a
number of 2 to 4.
[0017] Preferred polyaziridines are those in which
X=--(CH.sub.2).sub.n--O--CO--(CH.sub.2).sub.1--
[0018] where n=1 to 3, 1=1 to 3, and m=3 and R is a
CH.sub.3--CH.sub.2--C radical.
[0019] Another preferred polyfunctional aziridines are those in
which
X=--(CH.sub.2).sub.n--O--CO--(CH.sub.2).sub.1--
[0020] where n=1, 1=2, and m=3 and R is an OH --CH..sub.2--C
radical.
[0021] The polyfunctional aziridine useful herein is preferably
tri- or more highly functional compounds. The preferred materials
include: pentaerythritol-tris-(beta-(N-aziridinyl)propionate);
trimethylol-propane-tris-(.beta.-(N-aziridinyl)propionate); and
mixtures thereof. Ethylenimine Technologies (EIT) sell
representative polyfunctional aziridines under the trade name
XAMA.RTM.-7 and XAMA.RTM.-2, which are particularly preferred in
the present invention.
[0022] The polyfunctional aziridine is typically utilized in an
amount of at least 0.1% by weight percent of the UV curable coating
in the present invention. The polyfunctional aziridine is
preferably utilized in an amount from about 0.1% to 15%, with 0.5%
to 8% specially preferred, by weight percent of the UV curable
coating in the present invention. The polyfunctional aziridine
contributes to the adhesion of the UV curable coating to the golf
ball cover. However, the use of a high amount of polyfunctional
aziridine might cause the UV coating to undergo yellowing after
cure. Surface treatments, such as vibratory abrasion and corona or
plasma treatment, or other methods that result in surface
modifications to the golf ball cover, may be used to enhance
adhesion of the topcoat to the golf ball cover.
[0023] One of the UV reactive components in the present invention
is an UV curable oligomer. Proper selection of the oligomer is
important to obtaining the desired physical properties of the
resulting coating. The suitable UV curable oligomers in the present
invention are those oligomers containing acrylate functionality,
namely an acrylate double bond. The double bond can open to form a
crosslinked polymer network when irradiated with UV light in the
presence of photo-initiators. The suitable UV reactive components
in the present invention include urethane acrylate, epoxy acrylate,
polyether acrylate or polyester acrylate, and are known in the art.
However the polyether and polyester acrylates must be low in acid
content, such as an acid number of less than 10, preferably less
than 5, to avoid premature reaction with the polyaziridine
component. In general, urethane acrylate oligomers impart toughness
and abrasion resistance to the final coatings, while epoxy acrylate
oligomers and polyester acrylate oligomers impart hardness and
chemical resistance. The UV curable acrylate component will consist
of between 30 to 80 weight percentage of the total composition
weight of the UV-curable coating. The polyether acrylates
advantageously have a low viscosity, preferably in the range of
about 75 to about 250 centipoise. Examples of commercially
available oligoether acrylates include LR 8967, and 8863, which are
all available from BASF.
[0024] The preferred UV curable component of the invention is
urethane acrylate oligomers formed by the reaction of an isocyanate
group, and an acrylic monomer having at least one hydroxyl group.
Preferred acrylic monomers include hydroxyethyl acrylate,
hydroxypropyl acrylate and caprolactone acrylate. Suitable
isocyanates include aliphatic isocyanates, cycloaliphatic
isocyanates, alkaryl isocyanates, arylalkyl heterocyclic
isocyanates and aryl isocyanates. Suitable isocyanates of the
invention could be monoisocyanates, diisocyanates, or
triisocyanates. The diisocyanates are the preferred isocyanates of
the invention.
[0025] Examples of diisocyanates include tetramethylene
diisocyanate,pentamethylene diisocyanate, octomethylene
diisocyanate, dodecylmethylenediisocyanate,
3,3-diisocyanatodipropyl ether, xylylene diisocyanate,
meta-phenylenediisocyanate, 1-methylphenylene-2,4-diisocyan- ate,
2,6-toluenediisocyanate, 2,6-toluene diisocyanate,
cyclohexane-1,4-diisocyanate,methane-bis(cyclohexy-4-isocyanate),
and isophorone diisocyanate.
[0026] Preferred diisocyanates include Tolylene diisocyanate (TDI),
Hexamethylene diisocyanates (HDI), ), Norbornane diisocyanates
(NBDI), Isophorone diisocyanates (IPDI), Diphenylmethane
diisocyanates (MDI), bis(4-isocyanatocyclohexyl) methane
(Desmodur.RTM. W) and Polyisocyanates from HDI (Desmodur.RTM.
N-100, Desmodur.RTM. N-3200, Desmodur.RTM. N3300). Aliphatic
diisocyanates are the most preferred diisocyanates of the invention
because of their non-yellowing characteristics.
[0027] In one preferred embodiment, urethane acrylate oligomers are
formed by reacting an aliphatic diisocyanate with hydroxy monomer
in stoichiometric proportions and further reacting this with a long
chain polyol to form a flexible urethane acrylate oligomer.
[0028] Oligomers of molecular weight greater than 8000 can produce
a coating with too much flexibility, while oligomers of molecular
weight below 500 produce a coating that has low impact resistance.
Preferably, the oligomers used in the present invention have
molecular weights ranging from 500 to 8000, with preferred range
from 500 to 5000. The urethane acrylate oligomer should be utilized
in an amount ranging from about 30% to 80% by weight percent of the
total coating, and more preferably, between 40% to 70% by weight
percent of the total coating.
[0029] The urethane polyacrylate oligomer UV curable component has
a relatively low viscosity, preferably in the range of about 8,000
to about 40,000 centipoise. The aliphatic urethane polyacrylate
oligomer component provides the abrasion resistance and the
resiliency of the polyurethane coating. As illustrative and
non-limiting examples, the aliphatic urethane polyacrylate oligomer
component are sold by companies such as Sartomer Company Inc., or
under the BOMAR.RTM. designation by Bomar Specialties, Winsted,
Conn.
[0030] In the preparation of an UV curable coating, the UV-curable
oligomer is typically utilized in combination with a reactive
diluent system. Broadly, suitable reactive diluent systems comprise
at least one unsaturated addition polymerizable monomer, which is
copolymerizable with the UV-curable oligomer upon exposure to
radiation. The reactive diluent can be monofunctional, difunctional
or polyfunctional. A single polyfunctional diluent can be used; or
a combination of one or more monofunctional reactive diluents, one
or more difunctional reactive diluents, and one or more
polyfunctional reactive diluents can be used.
[0031] Particularly preferred reactive diluents are unsaturated
addition-polymerizable monofunctional, difunctional and
polyfunctional acrylic monomers. Acrylate monomers useful as a
reactive diluent system are well known and examples of such
monomers include isobornyl acrylate, phenoxyethyl acrylate,
isodecyl acrylate, hexyl acrylate, cyclohexyl acrylate,
2-ethylhexyl acrylate, octyl acrylate, nonyl acrylate, stearyl
acrylate, 2-phenoxy acrylate, 2-methoxyethyl acrylate, lactone
modified esters of acrylic and methacrylic acid, methyl
methacrylate, butyl acrylate, isobutyl acrylate, methacrylamide,
allyl acrylate, tetrahydrofuryl acrylate, n-hexyl methacrylate,
2-(2-ethoxyethoxy)ethyl acrylate, n-lauryl acrylate, 2-phenoxyethyl
acrylate, glycidyl methacrylate, glycidyl acrylate, acrylated
methylolmelamine, 2-(N,N-diethylamino)-ethyl acrylate, neopentyl
glycol diacrylate, alkoxylated neopentyl glycol diacrylate,
ethylene glycol diacrylate, hexylene glycol diacrylate, diethylene
glycol diacrylate, tripropylene glycol diacrylate, tetraethylene
glycol diacrylate, pentaerythritol di-, tri-, tetra-, or
penta-acrylate, trimethylolpropane triacrylate, alkoxylated
trimethylol-propane triacrylate which contains from 2 to 14 moles
of either ethylene or propylene oxide, triethylene glycol
diacrylate, tetraethylene glycol diacrylate, polyethylene glycol
diacrylate, 1,3-butylene glycol diacrylate, 1,4-butanediol
diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol
diacrylate, combinations thereof, and any corresponding
methacrylates thereof.
[0032] The reactive diluent system typically comprises from about
10 to 60, preferably from about 20 to 50 percent by weight of the
total UV curable coating. The photo-initiator can be any of the
known photo-initiators. Specific examples include benzophenone,
benzoin, acetophenone, benzoin methyl ether, Michler's ketone,
benzoin butyl ether, xanthone, thioxanthone, propiophenone,
fluorenone, carbozole, diethyoxyacetophenone, the 2-, 3- and 4-
methylacetophenones and methoxyacetophenones, the 2- and
3-chloroxanthones and chlorothioxanthones, 2-acetyl-4-methylphenyl
acetate, 2,2'-dimethyoxy-2-phenyl acetophenone, benzaldehyde,
fluorene, anthraquinone, triphenylamine, 3- and
4-allyl-acetophenone, p-diacetylbenzene, 3-chloro-2-nonylxanthone,
2-chlorobenzophenone, 4-methoxybenzophenone,
2,2',4,4'-tetrachlorobenzophenone, 2-chloro-4'-methylbenzophenone,
4-chloro-4'-methylbenzophenone, 3-methylbenzophenone,
4-tert-butyl-benzophenone, isobutyl ether, benzoic acetate, benzil,
benzilic acid, amino benzoate, methylene blue,
2,2-diethoxyacetophenone, 9,10-phenanthrenequinone, 2-methyl
anthraquinone, 2-ethyl anthraquinone, 1-tert-butyl-anthraquinone,
1,4-naphthoquinone, isopropylthioxanthone, 2-chlorothioxanthone,
2-iso-propylthioxanthone, 2methylthioxanthone, 2-decylthioxanthone,
2-dodecyl-thioxanthone, 2-methyl- 1-[4-(methyl
thio)phenyl)]-2-morpholino- propanone-1, combinations thereof and
the like. The photo-initiator or combination of photo-initiators is
typically utilized in an amount ranging from about 0.5 to 15,
preferably from about 1 to 8 percent by weight of the UV curable
coating in the present invention. The peak absorbance is typically
in the range of about 240 nm to about 390 nm.
[0033] In general, exemplary monomers, oligomers, and
photoinitiators can be found in "Chemistry and Technology of UV and
EB Formulations for Coatings, Paints, and Inks", P. K. T. Oldring,
ed., (1991), ISBN 0 947798 10.2.
[0034] An UV curable coating, comprising at least one UV reactive
component, a polyfunctional aziridine, and a photo-initiator of the
present invention, may also contain other optional ingredients
known to those skilled in the art of UV curable compositions. An
optional ingredient is a whitener that improves the overall
appearance of the UV curable coating. Suitable whiteners include
2,5-Bis (5 tert-butyl-2-benzoxazolyl) thiophene (Uvitex.RTM. OB
from Ciba Specialty Chemical Co.), 7-(2h-napthol
(1,2-d)-triazol-2-yl)-3-phenyl-coumarin (Leucopure.RTM. EGM from
Clariant).
[0035] Other optional components of the present UV curable coating
include surfactants to modify the flow and wetting characteristics
of the coating
[0036] The UV curable coating as described above of the present
invention contains more than 90%, preferably greater than 95%
solids, more preferably more than 98% solids, and most preferably
essentially 100% solids. The UV curable outer coating is
substantially solvent free (<5%) by weight, preferably less than
2% of volatile organic solvent. Most preferably the coating is
essentially solvent-free which avoids the problems of energy
consumption in evaporating the solvent, solvent pollution, and the
cost of solvent. However, the present UV curable coating can also
be diluted with solvent for improved application to various
substrates if desired. The choice of solvent employed for dilution
is not critical. Preferred solvents are those that are classified
as exempt from (volatile organic component) VOC classification such
as acetone. However VOC containing solvents can also be used. For
instance, 10% solvent may be incorporated to reduce the viscosity
of the UV curable coating in order to carry out the desired
performance of spraying.
[0037] UV curable coatings can be applied to a substrate to be
coated or bonded by various techniques well known in the art e.g.
roll coater, curtain coater, vacuum coater, and spray to form a
coating thickness in the range of 0.1 mils to 3.0 mils, preferably
0.2 to 1.0 mils. The coating is particularly advantageous for
polymeric substrates including polyvinyl chloride, either rigid or
flexible PVC, polycarbonates as the hard to adhere polymers such as
polypropylene and polyethylene, as well as the thermoplastic
vulcanizates, and thermoplastic olefins (TPO).
[0038] Solvents can be added to aid in application if necessary.
After application of the coating to a substrate, polymerization of
the coating is initiated. The polymerization may be initiated by
any method or means known in the art for initiating
radiation-curable materials. At the present invention, it is
preferred to initiate polymerization of the coating by exposing the
coating to any source of actinic radiation at a wavelength within
the ultraviolet or visible spectral regions. Suitable sources of
radiation include mercury, xenon, carbon arc and tungsten filament
lamps, sunlight, etc. Exposures may be from less than about 0.1
second to 10 minutes or more depending upon the amounts of
particular polymerizable materials and photo-initiators being
utilized and depending upon the radiation source and distance from
the source. The compositions may also be polymerized by exposure to
electron beam irradiation in a dosage typically ranging from less
than about 1 megarad to 100 megarad or more. The use of thermal
energy during or after exposure to a radiation source will also
generally accelerate the curing reaction, and even a moderate
increase in temperature may greatly accelerate cure rate.
[0039] An UV curable coating of the present invention can be used
in essentially any type of coating or adhesive application known in
the art. In particular, though not exclusively, the UV curable
coating is particularly suitable for golf ball application, wherein
the golf ball comprises an ionomer resin layer.
[0040] Typical golf ball cover materials and compositions include
thermoplastic ionomer resins such as those sold under the
trademarks SURLYN.RTM., available from E.I. Du Pont de Nemours and
Co., Wilmington, Del.; or IOTEK.RTM., available from Exxon Chemical
Co., Polymers Group, Baytown, Tex.
[0041] The UV curable coating in the invention has enhanced
adhesion to the ionomer substrates, such as SURLYN.RTM. resin.
Adhesion was tested by using Cross-hatch test method. Adhesion of
an UV coating without polyaziridine varied from 4% to 97% depending
on the surface treatment. Adhesion was improved to 100% after
polyaziridine incorporated.
[0042] The following examples are provided for purposes of
illustrating the invention and should not be construed in any
manner to limit the scope of the invention, which is defined by the
claims.
EXAMPLE 1
[0043] A urethane acrylate oligomer is prepared as follows:
[0044] 1103 grams of Desmodur.RTM. W (commercially available from
Bayer) and 0.8 grams of toluhydroquinone are added into a reaction
kettle. The contents of the reaction kettle are heated to
50.degree. C. under dry air, and 724.2 grams of Tone.RTM. M-100
(commercially available from Union Carbide) and 2 drops of tin
catalyst are then added. The reaction kettle is heated to
50-60.degree. C. for 30 minutes, and then another 724.2 grams of
Tone.RTM. M-100 and 2 drops of T-9 catalyst are added into the
reaction kettle to form a mixture. The mixture is heated at
60-70.degree. C. for about 8 hours until NCO<0.25.
EXAMPLE 2
[0045] 45 g urethane acrylate oligomer as in Example 1, 49.7 g
acrylic monomers (a mixture of SR238, SR492 and SR256, which are
commercially available from Sartomer, Inc.), 0.1 g surfactant, and
1.5 g 1-hydroxycyclohexyl phenyl ketone (available from Ciba under
the tradename Irgacure.RTM. 184), 3 g benzophenone, and 0.2 g
fluorescent whitener (available from Ciba under the tradename
Uvitex.RTM. OB) were mixed until homogeneous. To this mixture was
added 0.5 g polyaziridine. The solution was mixed for another 15
minutes to afford a coating. The coating was then sprayed onto a
golf ball using HVLP spray techniques (High Volume Low Pressure).
The golf ball was then cured under a Fusion.RTM. UV lamp system.
The total cure energy used was 600 mj/cm.sup.2 cm.sup.2 in an air
atmosphere. The coating exhibited a high whiteness index and very
good adhesion on the golf ball surface. The golf balls were tested
in a cannon tester for 50 hits, and no micro cracking or loss of
adhesion was observed.
EXAMPLE 3
[0046] Formulations were prepared and cured as in Example 2. A
conventional adhesion promoter was added to enhance the adhesion of
the coating to the SURLYN.RTM. cover. This was ineffective. In 3-B,
3-C, and 3-D, a low level of polyaziridine adhesion promoter was
incorporated into the formulation. The incorporation of
polyaziridine into the formulation improved the adhesion of UV
coating from 5% to 100%.
1 TABLE I 3-A 3-B 3-C 3-D Urethane oligomer 50 g 50 g 50 g 50 g
Acrylate monomers 40.5 g 40.4 g 40.2 g 40 g Adhesion promoter THF
acrylate 5 g 5 g 5 g 5 g Polyaziridine 0 g 0.1 g 0.3 g 0.5 g
Photoinitiators 4.5 g 4.5 g 4.5 g 4.5 g Adhesion* 5% 100% 100% 100%
*Tested on SURLYN plaque using a cross-hatch adhesion test.
EXAMPLE 4
[0047] Formulations based on Example 2 were prepared with varied
levels of benzophenone. The coatings were applied onto flat plaques
of SURLYN.RTM. cover and cured as in Example 2. As can be seen from
the data in the Table II below increasing the level of benzophenone
will increase the whiteness index of the coating.
2TABLE II Benzophenone Coating (% by weight) Whiteness index* 2-A
3% 118.28 2-B 2% 114.89 2-C 0 110.50 Whiteness index = -3b* + L
* * * * *