U.S. patent application number 11/235624 was filed with the patent office on 2007-03-22 for dual cure compositions, methods of curing thereof and articles therefrom.
Invention is credited to Paul Takao Furuta, Wendy Wen-Ling Lin, Wenliang Patrick Yang.
Application Number | 20070066698 11/235624 |
Document ID | / |
Family ID | 37452148 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070066698 |
Kind Code |
A1 |
Yang; Wenliang Patrick ; et
al. |
March 22, 2007 |
Dual cure compositions, methods of curing thereof and articles
therefrom
Abstract
Disclosed herein are dual cure compositions, methods to cure
dual cure compositions, the dual cure compositions comprising at
least one filler, at least one curable monomer comprising at least
one of an ethylenic unit or cyclic ether unit or mixture thereof;
at least one photoinitiator; and at least one thermal initiator.
The method comprises the step of photocuring by exposing the
compositions to radiation to at least partially photocure the
composition, which in turn generates an exotherm which initiates
thermal curing. The methods may be used to make cured thick
compositions and sandwich structures. Articles made by the methods
are also described.
Inventors: |
Yang; Wenliang Patrick;
(Ballston Lake, NY) ; Lin; Wendy Wen-Ling;
(Niskayuna, NY) ; Furuta; Paul Takao; (Niskayuna,
NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY;GLOBAL RESEARCH
PATENT DOCKET RM. BLDG. K1-4A59
NISKAYUNA
NY
12309
US
|
Family ID: |
37452148 |
Appl. No.: |
11/235624 |
Filed: |
September 20, 2005 |
Current U.S.
Class: |
522/6 |
Current CPC
Class: |
C09D 4/00 20130101; B32B
5/26 20130101; B32B 27/04 20130101; C08K 3/36 20130101; B32B 27/12
20130101; B32B 27/30 20130101; C08F 2/48 20130101; B32B 9/00
20130101; C08K 7/14 20130101; B32B 5/18 20130101; C08J 5/24
20130101; B32B 5/28 20130101; B32B 17/04 20130101; C08J 2363/00
20130101 |
Class at
Publication: |
522/006 |
International
Class: |
C08F 2/50 20060101
C08F002/50 |
Claims
1. A dual cure composition having structural units derived from a
composition comprising: at least one UV opaque filler; at least one
curable monomer comprising at least one ethylenic unit or cyclic
ether unit or mixture thereof; at least one photoinitiator; and at
least one thermal initiator.
2. The composition of claim 1, wherein the UV opaque filler is
selected from the group consisting of carbon fibers, carbon black,
carbon nanotubes, silicon carbide, boron nitride, titanium dioxide,
zirconium oxide, chalk, calcium sulfate, barium sulfate, calcium
carbonate, silicates, talc, mica, kaolin, silica, aluminum
hydroxide, magnesium hydroxide, polymer powder, polymer fiber, and
mixtures thereof.
3. The composition of claim 1, wherein the curable monomer is
selected from the group consisting of an unsaturated polyester, a
vinyl ester, an acrylate, a methacrylate, a diacrylate, a
dimethacrylate, a multifunctional acrylate, a multifunctional
methacrylate, an epoxide, an oxetane, a multifunctional epoxide, a
multifunctional oxetane, and mixtures thereof.
4. The composition of claim 1, wherein the photoinitiator comprises
an organic peroxide, an azo compound, a quinone, a benzophenone, a
nitroso compound, an acryl halide, a hydrozone, a mercapto
compound, a pyrylium compound, a triacrylimidazole, a bisimidazole,
a chloroalkyltriazine, a benzoin ether, a benzil ketal, a
thioxanthone an acetophenone, an acylphosphine oxide, an onium
salt, a derivative of one of the aforementioned compounds, or
mixtures thereof.
5. The composition of claim 1, wherein the photoinitiator is
present in a range of from about 0.01 weight percent to about 20
weight percent, based on the weight of the curable monomer.
6. The composition of claim 1, wherein the filler is present in a
range of from about 1 weight percent to about 90 weight percent,
based on the total weight of the composition.
7. The composition of claim 1, wherein the thermal initiator
comprises benzoyl peroxide, dicumyl peroxide, methyl ethyl ketone
peroxide, lauryl peroxide, cyclohexanone peroxide, t-butyl
hydroperoxide, t-butyl benzene hydroperoxide, t-butyl peroctoate,
2,5-dimethylhexane-2,5-dihydroperoxide,
2,5-dimethyl-2,5-di(t-butylperoxy)-hex-3-yne, di-t-butylperoxide,
t-butylcumyl peroxide,
.alpha.,.alpha.'-bis(t-butylperoxy-m-isopropyl)benzene,
2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di(t-butylperoxy)
isophthalate, t-butylperoxy benzoate, 2,2-bis(t-butylperoxy)butane,
2,2-bis(t-butylperoxy)octane,
2,5-dimethyl-2,5-di(benzoylperoxy)hexane,
di(trimethylsilyl)peroxide, trimethylsilylphenyltriphenylsilyl
peroxide, 2,3-dimethyl-2,3-diphenylbutane,
2,3-trimethylsilyloxy-2,3-diphenylbutane, copper(II)
acetylacetonate, palladium(II) acetylacetonate, ruthenium(III)
acetylacetonate, an onium salt, a sulfonium salt, an iodonium salt,
or mixtures thereof.
8. The composition of claim 1, wherein the thermal initiator is
present in a range of from about 0.01 weight percent to about 10
weight percent based on the weight of the curable monomer.
9. The composition of claim 1, further comprising at least one
additive selected from the group consisting of photosensitizers,
pigments, tackifiers, UV transparent fillers, and mixtures
thereof.
10. A method of curing a dual cure composition comprising the steps
of: (i) providing a dual cure composition comprising: at least one
filler; at least one curable monomer comprising at least one of an
ethylenic unit or cyclic ether unit or mixture thereof; at least
one photoinitiator; and at least one thermal initiator; (ii)
exposing the composition to radiation of a wavelength made
available from a radiation source to at least partially photocure
the composition and to provide an exotherm sufficient to complete
the curing of the composition by thermal curing; and (iii) then
turning off the radiation source before complete curing is
achieved.
11. The method of claim 10, wherein the radiation comprises a
radiation wavelength sufficient to provide the exotherm.
12. The method of claim 11, wherein the radiation wavelength is in
the range of from about 200 nanometers to about 1000
nanometers.
13. The method of claim 10, wherein the exposing occurs for a time
sufficient to provide the exotherm.
14. The method of claim 10, wherein the exposing occurs for a time
period in the range of from about 1 second to about 5 hours.
15. The method of claim 10, wherein the composition is fully
cured.
16. An article made by the method of claim 10.
17. An article with thickness greater than 1 centimeter made by the
method of claim 10.
18. A body panel, truck bed, protective plate, fender, spoiler,
hood, door, lamp reflector, sanitary article, household implement,
house door, house window, furniture, coil, container, radiator,
electric motor coil, a wind rotor blade for wind turbine, an
aerospace article, a bridge component, a marine article, a sporting
goods article, a pipe, or a missile component made by the method of
claim 10.
19. A method of making a cured dual cure composition comprising the
steps of: (i) providing a dual cure composition comprising: at
least one filler comprising glass fibers, fumed silica, or
combinations thereof; at least one curable monomer comprising at
least one of an ethylenic unit or cyclic ether unit or mixture
thereof; at least one photoinitiator; and at least one thermal
initiator; and (ii) exposing the dual cure composition to radiation
of a wavelength made available from a radiation source to at least
partially photocure the composition, and to provide an exotherm
sufficient to initiate thermal curing to form a cured composition;
wherein the cured composition is at least 6 millimeters thick.
20. The method of claim 19, wherein the radiation source is turned
off before complete curing is achieved.
21. A method of making a cured dual cure composition comprising:
(i) providing a dual cure composition comprising: at least one UV
opaque filler comprising carbon fibers, carbon black, carbon
nanotubes, silicon carbide, boron nitride, titanium dioxide,
zirconium oxide, chalk, calcium sulfate, barium sulfate, calcium
carbonate, silicates, talc, mica, kaolin, silica, aluminum
hydroxide, magnesium hydroxide, polymer powder, polymer fiber, or
combinations thereof; at least one curable monomer comprising at
least one of an ethylenic unit or cyclic ether unit or mixture
thereof; at least one photoinitiator; and at least one thermal
initiator; and (ii) exposing the dual cure composition to radiation
of a wavelength made available from a radiation source to at least
partially photocure the composition, and to provide an exotherm
sufficient to initiate thermal curing to form a cured composition;
wherein the cured composition is at least 0.1 millimeter thick.
22. The method of claim 21, wherein the radiation source is turned
off before complete curing is achieved.
23. A method of curing a dual cure sandwich structure comprising
the steps of: (i) providing a dual cure composition comprising: at
least one reinforcing filler core comprising foam, slitted foam,
wood, honeycomb, or combinations thereof; at least one curable
monomer comprising at least one of an ethylenic unit or cyclic
ether unit or mixture thereof; at least one photoinitiator; and at
least one thermal initiator; and (ii) exposing the dual cure
composition to radiation of a wavelength made available from a
radiation source to at least partially photocure the composition,
and to provide an exotherm sufficient to initiate thermal curing to
form a cured composition.
24. The method of claim 23, wherein the radiation source is turned
off before complete curing is achieved.
25. A method of curing a dual cure composition comprising the steps
of: (i) providing a dual cure composition comprising: at least one
filler; at least one curable monomer comprising a vinyl ester; at
least one photoinitiator comprising a phosphorus compound; and at
least one thermal initiator comprising a peroxide compound; and
(ii) exposing the dual cure composition to radiation of a
wavelength made available from a radiation source to at least
partially photocure the composition, and to provide an exotherm
sufficient to initiate thermal curing to form an at least partially
cured composition.
26. The method of claim 25, wherein the radiation source is turned
off before complete curing is achieved.
27. The method of claim 25, wherein the composition is fully
cured.
28. A wind rotor blade for a wind turbine made by the method of
claim 25.
29. A wind rotor blade for a wind turbine made by the method of
claim 27.
Description
BACKGROUND
[0001] The invention relates generally to dual cure compositions,
methods of curing, and resulting articles.
[0002] Formation of thick sections by curing of thermoset resins
(sometimes referred to hereinafter as curable monomers) has been
generally problematic. Most traditional thermally cured reactive
formulations have short work-life and long cure time. On the other
hand, photocured formulations have long work-life and are capable
of rapid cure, but curing is limited by the penetration depth of UV
light, especially in materials with high levels of fillers which
absorb or block UV light, such as in thick section composites,
composite sandwich structures, and carbon fiber composites, thus
resulting in uncured or incompletely cured portions. Curing thick
carbon fiber composites has been demonstrated with e-beam
technology. However, e-beam uses a high energy source which
requires high cost capital investment.
[0003] The problems described have been addressed by the use of
compositions comprising monomers that are cured by one or more
energy sources. The cured compositions are typically derived from
monomers having ethylenic units, isocyanate units, ester units, or
the like, or combinations thereof. Curing of some of the
compositions results in evolution of gases, which may become
entrapped in the composition thus compromising some of the
properties of the product. Also, the curing methods result in
inefficient energy usage. Alternatively, thick sections have been
formed by joining multiple precured panels or plies. But this
results in bond lines. Thus, there is a need in the art to develop
novel curable compositions and more efficient and cost-effective
methods to fabricate thick sections, structures and articles.
BRIEF DESCRIPTION
[0004] In one embodiment, the invention provides a cured dual cure
composition comprising at least one UV opaque filler; at least one
curable monomer comprising at least one of an ethylenic unit or
cyclic ether unit or mixture thereof; at least one photoinitiator;
and at least one thermal initiator.
[0005] In another embodiment, the invention provides a method of
curing a dual cure composition comprising the steps of: (i)
providing a dual cure composition comprising at least one filler;
at least one curable monomer comprising at least one of an
ethylenic unit or cyclic ether unit or mixture thereof; at least
one photoinitiator; and at least one thermal initiator; (ii)
exposing the composition to radiation of a wavelength made
available from a radiation source to at least partially photocure
the composition and to provide an exotherm sufficient to complete
the curing of the composition by thermal curing; and (iii) then
turning off the radiation source before complete curing is
achieved.
[0006] In yet another embodiment, the invention provides a method
of making a cured dual cure composition comprising the steps of (i)
providing a dual cure composition comprising at least one filler
comprising glass fibers, fumed silica, or combinations thereof; at
least one curable monomer comprising at least one of an ethylenic
unit or cyclic ether unit or mixture thereof; at least one
photoinitiator; and at least one thermal initiator; and (ii)
exposing the dual cure composition to radiation of a wavelength
made available from a radiation source to at least partially
photocure the composition, and to provide an exotherm sufficient to
initiate thermal curing to form a cured composition; wherein the
cured composition is at least 6 millimeters thick.
[0007] In still another embodiment, the invention provides a method
of making a cured dual cure composition comprising (i) providing a
dual cure composition comprising at least one UV opaque filler
comprising carbon fibers, carbon black, carbon nanotubes, silicon
carbide, boron nitride, titanium dioxide, zirconium oxide, chalk,
calcium sulfate, barium sulfate, calcium carbonate, silicates,
talc, mica, kaolin, silica, aluminum hydroxide, magnesium
hydroxide, polymer powder, polymer fiber, or combinations thereof;
at least one curable monomer comprising at least one of an
ethylenic unit or cyclic ether unit or mixture thereof; at least
one photoinitiator; and at least one thermal initiator; and (ii)
exposing the dual cure composition to radiation of a wavelength
made available from a radiation source to at least partially
photocure the composition, and to provide an exotherm sufficient to
initiate thermal curing to form a cured composition; wherein the
cured composition is at least 0.1 millimeter thick.
[0008] In a further embodiment, the invention provides a method of
curing a dual cure sandwich structure comprising the steps of (i)
providing a dual cure composition comprising at least one
reinforcing filler core comprising foam, slitted foam, wood,
honeycomb, or combinations thereof; at least one curable monomer
comprising at least one of an ethylenic unit or cyclic ether unit
or mixture thereof; at least one photoinitiator; and at least one
thermal initiator; and (ii) exposing the dual cure composition to
radiation of a wavelength made available from a radiation source to
at least partially photocure the composition, and to provide an
exotherm sufficient to initiate thermal curing to form a cured
composition. Other embodiments of the invention comprise articles
made by the methods described.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings.
[0010] FIG. 1 shows the temperature profile at the center of two
formulations in an embodiment of the invention as determined by an
embedded thermocouple. The solid line shows the temperature profile
of the formulation obtained by exposing the composition to
radiation of a wavelength made available from a radiation source to
at least partially photocure the composition and to provide an
exotherm sufficient to complete the curing of the composition by
thermal curing. The dashed line shows the temperature profile of
the formulation that was not exposed to a radiation source.
[0011] FIG. 2 shows the temperature profile at the center of a
formulation in an embodiment of the invention as determined by an
embedded thermocouple, wherein during the curing stage, the
radiation source was shut off after an exotherm was initiated but
before the peak temperature was achieved.
[0012] FIG. 3 shows a representative sandwich structure prepared in
an embodiment of the invention.
DETAILED DESCRIPTION
[0013] Disclosed herein are compositions that may be cured by a
combination of photocuring and thermal curing methods. The
compositions comprise at least one filler, at least one curable
monomer comprising at least one of an ethylenic unit or cyclic
ether unit or mixture thereof, at least one photoinitiator, and at
least one thermal initiator. As used herein, ethylenic unit refers
to a compound comprising a carbon atom linked to another carbon
atom through a double bond, and cyclic ether refers to a compound
comprising an oxygen atom linked to carbon atoms and comprising a
ring structure. In the specification and the claims which follow,
singular forms "a", "an" and "the" include plural referents unless
the context clearly dictates otherwise.
[0014] Fillers which may be present in compositions of the
invention comprise organic or inorganic fillers, reinforcing
fillers, extending fillers, nanoparticles, or the like, or mixtures
thereof. In particular embodiments the filler generally comprises a
reinforcing filler, such as, but not limited to, a fiber having
high strength. The strength of the fibers may be further increased
by using techniques known in the art, such as, but not limited to,
forming a plurality of layers or plies, by orientation of the
fibers in a direction, and like methods. The fibers may be made
available in any conventional form such as, braided,
unidirectional, woven fabric, knitted fabric, swirl fabric, felt
mat, wound, and the like. Exemplary fibers that may be
advantageously used in the invention comprise carbon fibers (e.g.
TORAYCA.RTM. T800, TORAYCA.RTM. T700, and TORAYCA.RTM. T600 from
Toray Industries, Inc.; MAGNAMITE.RTM. IM7 and MAGNAMITE.RTM. AS4
from Hexcel Corporation; and BESFIGHT.RTM. STS and BESFIGHT.RTM.
HTS from Toho Tenax, Inc.), glass fibers (e.g. quartz, E-glass, S-2
glass, R-glass from suppliers such as PPG, AGY, St. Gobain,
Owens-Corning, or Johns Manville), polyester fibers, polyamide
fibers (such as NYLON.TM. polyamide available from E.I. DuPont,
Wilmington, Del., USA), aromatic polyamide fibers (such as
KEVLAR.TM. aromatic polyamide available from E.I. DuPont,
Wilmington, Del., USA; or P84.TM. aromatic polyamide available from
Lenzing Aktiengesellschaft, Austria), polyimide fibers (such as
KAPTON.TM. polyimide available from E.I. DuPont, Wilmington, Del.,
USA), extended chain polyethylene (such as SPECTRA.TM. polyethylene
from Honeywell International Inc., Morristown, N.J., USA; or
DYNEEMA.TM. polyethylene from Toyobo Co., Ltd., or DSM, boron
fibers, and the like. The fillers may be UV transparent fillers
such as, but not limited to, glass, silica, fumed silica, alumina,
zirconium oxide, nanoparticles, and the like. Alternately, the
fillers may be UV opaque fillers such as, but not limited to,
carbon fibers, carbon black, silicon carbide, boron nitride,
zirconium oxide, titanium dioxide, chalk, calcium sulfate, barium
sulfate, calcium carbonate, silicates such as talc, mica or kaolin,
silicas, aluminum hydroxide, magnesium hydroxide, or organic
fillers such as polymer powders, polymer fibers, or the like. In
the present context UV opaque means that the material either blocks
UV radiation, or absorbs UV radiation, or both. Those skilled in
the art will recognize that, depending upon such factors as
physical form or method of synthesis, certain fillers may be either
UV opaque or UV transparent. Mixtures of more than one filler are
also within the scope of the invention.
[0015] The filler is typically present in the composition in a
range of from about 1% to about 90%, and more typically in a range
of from about 10% to about 80% by weight, based on the total weight
of the composition. More preferably, the filler is present in a
range of from about 30% to about 75% by weight, based on the total
weight of the composition.
[0016] The composition comprises at least one curable monomer. In
some embodiments, the compositions typically comprise monomers
having at least one ethylenic unit, cyclic ether unit, or epoxide
unit, oxetane unit, or the like, or combinations thereof. In other
embodiments, the compositions typically comprise monomers having at
least one isocyanate unit, ester unit, or the like, or combinations
thereof. Suitable curable monomers comprise unsaturated polyester
such as POLYLITE.RTM. polyester resin available from Reichhold,
SYNOLITE.RTM. polyester resin available from DSM, AROPOL.TM.
polyester resin available from Ashland; vinyl esters such as
DION.RTM., NORPOL.RTM., and HYDREX.RTM. resins available from
Reichhold, DERAKANE.RTM., DERAKANE MOMENTUM.RTM. and HETRON.RTM.
resins available from Ashland, ATLAC E-NOVA.RTM. resin available
from DSM; acrylates, diacrylates, dimethacrylates, multi-functional
acrylates and multi-functional methacrylates such as polyester
acrylates, epoxy acrylates and urethane acrylates, and the like,
available from such companies as Cytec Surface Specialties,
Sartomer, Rahn, and BASF. The curable monomer is typically present
in a range of from about 90% by weight to about 10% by weight,
based on the total weight of the composition, and more preferably,
in a range of from about 80% by weight to about 20% weight, based
on the total weight of the composition.
[0017] Suitable resins comprising at least one cyclic ether unit
comprise aliphatic epoxy resins, cycloaliphatic epoxy resins such
as ERL-4221, CYRACURE.TM. UVR-6110, CYRACURE.TM. UVR-6107, and
CYRACURE.TM. UVR-6105 from Dow Chemical Company and UVACURE.RTM.
1500 from Cytec Surface Specialties; bisphenol-A epoxy resins,
bisphenol-F epoxy resins, phenol novolac epoxy resins,
cresol-novolac epoxy resins, biphenyl epoxy resins,
multi-functional epoxy resins (i.e. epoxy resins comprising two or
more epoxy groups), naphthalene epoxy resins (e.g., EPICLON.RTM.
EXA-4700 from Dainippon Ink and Chemicals), divinylbenzene dioxide,
2-glycidylphenylglycidyl ether, dicyclopentadiene-type epoxy resins
(e.g., EPICLON.RTM. HP-7200 from Dainippon Ink and Chemicals),
multi-aromatic resin type epoxy resins, or the like, or
combinations thereof. All of these classes of epoxy resins are
known in the art and are widely available and preparable by known
methods. Other illustrative examples of particular suitable epoxy
resins and curing processes are described, for example, in U.S.
Pat. Nos. 4,882,201, 4,920,164, 5,015,675, 5,290,883, 6,333,064,
6,518,362, 6,632,892, 6,800,373; U.S. Patent Application
Publication No. 2004/0166241, and WO 03/072628 A1. Multi-functional
oxetane resins are also within the scope of the invention.
[0018] In some embodiments photoinitiators used in the invention
generate free radicals when exposed to radiation of wavelength at
which the photoinitiators are active. In other embodiments suitable
photoinitiators generate acid (photoacid generators, or PAGs) when
exposed to radiation of wavelength at which the photoinitiators are
active. Different types of photoinitiators can be used alone or as
mixtures. In a particular embodiment a photoacid generator can be
used together with a radical photoinitiator to initiate the curing
of cationic curable monomers Suitable photoinitiators include, but
are not limited to, organic peroxides, azo compounds, quinones,
benzophenones, nitroso compounds, acryl halides, hydrazones,
mercapto compounds, pyrylium compounds, triacrylimidazoles,
bisimidazoles, chloroalkyltriazines, benzoin ethers, benzil ketals,
thioxanthones, acetophenones, acylphosphine oxides, derivatives of
the aforementioned compounds, and mixtures thereof. Exemplary
photoinitiators comprise: benzil ketals such as
2,2-dimethoxy-2-phenyl acetophenone (available from Ciba Specialty
Chemicals under the trademark IRGACURE.RTM. 651); acetophenone
derivatives such as 2,2-diethoxyacetophenone ("DEAP", available
from First Chemical Corporation);
2-hydroxy-2-methyl-1-phenyl-propan-1-one ("HMPP", available from
Ciba Specialty Chemicals under the trademark DAROCUR.TM. 1173);
2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone
(available from Ciba Specialty Chemicals under the trademark
IRGACURE.TM. 369);
2-methyl-1-(4-(methylthio)phenyl)-2-morpholinopropan-1-one
(available from Ciba Specialty Chemicals under the trademark
IRGACURE.RTM. 907); or acylphosphine oxides such as
2,4,6-trimethylbenzoyl diphenylphosphine oxide ("TPO"),
bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide
("DMBAPO"), or bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide
("BTBPPO"). BTBPPO is available from Ciba Specialty Chemicals under
the trademark IRGACURE.RTM. 819; DMBAPO is available from Ciba
Specialty Chemicals in the form of blends with other ketones
including: 25/75 wt % blend with HMPP as IRGACURE.RTM. 1700, and
1-hydroxy-cyclohexyl-phenyl-ketone, (or HCPK) as IRGACURE.RTM. 1850
or 1800 depending on proportions. TPO is also available from Ciba
Specialty Chemicals in 50/50 wt % blends with HMPP (as
IRGACURE.RTM. 4265). In a preferred embodiment, photoinitiators
used are acylphosphine oxide type, most preferably IRGACURE.RTM.
819 available from Ciba Specialty Chemicals. Photoinitiators which
generate acid when exposed to radiation of wavelength at which the
photoinitiators are active include, but are not limited to, onium
salts, aryl sulfonium and aryl iodonium salts of weakly basic
anions, such as hexafluorophosphate or hexafluoroantimonate. Some
particular examples comprise (4-(octyloxy)phenyl)phenyliodonium
hexafluoroantimonate (OPPI) available from Hampford Research,
triarylsulfonium hexafluorophosphate;
[4-[(2-hydroxytetradecyl)oxy]phenyl]phenyliodonium
hexafluoroantimonate available from Aldrich; UVACURE.RTM. 1600 from
Cytec Surface Specialties, IRGACURE.RTM. 250 from Ciba Specialty
Chemicals, IGM-C445 from IGM Resins, Inc., Bartlett, Ill.;
CYRACURE.TM. UVI6992 and CYRACURE.TM. UVI6976 from Dow Chemicals;
ESACURE.RTM. 1064 and ESACURE.RTM. 1187 from Lamberti; R-gen 1130,
R-gen BF1172, CHIVACURE.RTM. 1176 and CHIVACURE.RTM. 1190 from
Chitec, and ferrocenium salts such as IRGACURE.RTM. 261 from Ciba
Specialty Chemicals.
[0019] Suitable amounts of photoinitiator are in a range of from
about 0.01% to about 20%, preferably in a range of from about 0.1%
to about 10%, and most preferably in a range of from about 0.5% to
about 5% by weight, based on the weight of the curable monomer.
[0020] The use of a photosensitizer to tune the activation
wavelength of the photoinitiator is also within the scope of the
invention. Typical photosensitizers include, but are not limited
to, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin
isopropyl ether, benzil (dibenzoyl), diphenyl disulfide,
tetramethyl thiuram monosulfide, diacetyl, azobisisobutyronitrile,
2-methyl-anthraquinone, 2-ethyl-anthraquinone,
2-tert-butylanthraquinone, thioxanthone derivatives such as
isopropyl-thioxanthone available from First Chemical Corporation
and 1-chloro-4-propoxy-thioxanthone available from Aceto
Corporation and the like.
[0021] Embodiments of the invention, as described herein, also
comprise the use of thermal initiators. In a particular embodiment
a suitable thermal initiator may comprise any compound capable of
producing free radicals at elevated temperatures. In addition a
suitable thermal initiator may comprise a compound which generates
acid at elevated temperatures. Mixtures of different types of
thermal initiators are also within the scope of the invention. In
some particular embodiments thermal initiators comprise peroxide or
non-peroxide based radical initiators. Examples of useful peroxide
initiators, comprise benzoyl peroxide, dicumyl peroxide, methyl
ethyl ketone peroxide, lauryl peroxide, cyclohexanone peroxide,
t-butyl hydroperoxide, t-butyl benzene hydroperoxide, t-butyl
peroctoate, 2,5-dimethylhexane-2,5-dihydroperoxide,
2,5-dimethyl-2,5-di(t-butylperoxy)-hex-3-yne, di-t-butylperoxide,
t-butylcumyl peroxide,
.alpha.,.alpha.'-bis(t-butylperoxy-m-isopropyl)benzene,
2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di(t-butylperoxy)
isophthalate, t-butylperoxy benzoate, 2,2-bis(t-butylperoxy)butane,
2,2-bis(t-butylperoxy)octane,
2,5-dimethyl-2,5-di(benzoylperoxy)hexane,
di(trimethylsilyl)peroxide, trimethylsilylphenyltriphenylsilyl
peroxide, and the like, and mixtures thereof. Suitable non-peroxide
initiators comprise 2,3-dimethyl-2,3-diphenylbutane,
2,3-trimethylsilyloxy-2,3-diphenylbutane, and the like, and
mixtures thereof. A preferred thermal initiator is a ketone
peroxide such as methyl ethyl ketone peroxide available from Norac,
Inc., Azusa, Calif., USA under the trade name NOROX.RTM. MEKP-9H.
Additionally, in some embodiments the photoinitiator and thermal
initiator may be same compound.
[0022] Thermal initiators which can generate acid at elevated
temperature comprise onium salts, or aryl sulfonium or aryl
iodonium salts of weakly basic anions, such as hexafluorophosphate
or hexafluoroantimonate. Additionally, thermal coinitiators which
facilitate the generation of acid by activating the onium salts at
lower temperatures comprise the radical thermal initiators e.g.
peroxides, azo compounds, or transition metal compounds, such as
copper(I) or copper(II) salts, copper(II) acetylacetonate,
palladium(II) acetylacetonate, or ruthenium(III) acetylacetonate,
available from Aldrich. In particular embodiments the activated
acid generators initiate cationic curing of cyclic ether
thermosets.
[0023] The thermal initiator is typically present in a range of
from about 0.01% by weight to about 10% by weight, preferably in a
range of from about 0.1% by weight to about 5% by weight, and more
preferably in a range of from about 1% by weight to about 3% by
weight, based on the weight of the curable monomer.
[0024] The compositions of the invention may further optionally
comprise one or more pigments in effective amounts. Optional
pigments may comprise one or more color pigments, effect pigments,
fluorescent pigments, electrically conductive pigments,
magnetically shielding pigments, metal powders, scratch-proofing
pigments, organic dyes, or the like, or mixtures thereof.
[0025] Examples of suitable effect pigments comprise metal flake
pigments such as aluminum bronzes, chromated aluminum bronzes, or
stainless steel bronzes, and also nonmetallic effect pigments, such
as pearlescent pigments or interference pigments, for example,
platelet-shaped effect pigments based on iron oxide with a color
from pink to brownish red, or liquid-crystalline effect
pigments.
[0026] Examples of suitable inorganic color pigments comprise white
pigments such as, but not limited to, titanium dioxide, zinc white,
zinc sulfide or lithopones; black pigments such as carbon black,
iron manganese black or spinel black; chromatic pigments such as
chromium oxide, chromium oxide hydrate green, cobalt green or
ultramarine green, cobalt blue, ultramarine blue or manganese blue,
ultramarine violet, cobalt violet or manganese violet, red iron
oxide, cadmium sulfoselenide, molybdate red, ultramarine red; brown
iron oxide, spinel phases, corundum phases or chrome orange; yellow
iron oxide, nickel titanium yellow, chrome titanium yellow, cadmium
sulfide, cadmium zinc sulfide, chrome yellow or bismuth vanadate,
or the like, or mixtures thereof.
[0027] Examples of suitable organic color pigments comprise monoazo
pigments, diazo pigments, anthraquinone pigments, benzimidazole
pigments, quinacridone pigments, quinophthalone pigments,
diketopyrrolopyrrole pigments, dioxazine pigments, indanthrone
pigments, isoindoline pigments, isoindolinone pigments, azomethine
pigments, indigo pigments, metal complex pigments, perinone
pigments, perylene pigments, phthalocyanine pigments aniline black,
or the like, or mixtures thereof. Examples of fluorescent pigments
comprise bis(azomethine) pigments.
[0028] Examples of suitable electrically conductive pigments
comprise titanium dioxide/tin oxide pigments or mica pigments.
Examples of magnetically shielding pigments comprise pigments based
on iron oxides or chromium dioxide. Examples of suitable metal
powders comprise powders of metals and metal alloys such as
aluminum, zinc, copper, bronze or brass.
[0029] The dual cure compositions of the invention may further
comprise one or more tackifiers. The term tackifier refers to
polymeric adhesives which increase the tack, i.e., the inherent
stickiness or self-adhesion, of the compositions so that after a
short period of gentle pressure they adhere firmly to surfaces.
Examples of suitable tackifiers comprise high-flexibility resins
such as, but not limited to, homopolymers of alkyl(meth) acrylates,
especially alkyl acrylates, such as poly(isobutyl acrylate) or
poly(2-ethylhexyl acrylate), which are sold under the brand names
ACRONAL.RTM. by BASF Aktiengesellschaft, ELVACITE.RTM. by Dupont,
NEOCRYL.RTM. by Avecia, and PLEXIGUM.RTM. by Rohm; linear
polyesters, as commonly used for coil coating and sold, for
example, under the brand names DYNAPOL.RTM. by Dynamit Nobel,
SKYBOND.RTM. by SK Chemicals, Japan, or under the commercial
designation LTW by Huls; linear difunctional oligomers, curable
with actinic radiation, with a number average molecular weight of
more than 2000, in particular from 3000 to 4000, based on
polycarbonatediol or polyester-diol, which are sold under the
designation CN 970 by Craynor or the brand name EBECRYL.RTM. by
UCB; linear vinyl ether homopolymers or copolymers based on ethyl,
propyl, isobutyl, butyl and/or 2-ethylhexyl vinyl ether, sold under
the brand name LUTONAL.RTM. by BASF Aktiengesellschaft; or
nonreactive urethane urea oligomers, which are prepared from
bis(4,4-isocyanatophenyl) methane, N,N-dimethylethanolamine or
diols such as propanediol, hexanediol or dimethylpentanediol and
which are sold, for example, by Reichhold under the brand name
SWIFT RANGE.RTM. or by Mitchanol International Ltd., U.K., under
the brand name SURKOPAK.RTM. or SURKOFILM.RTM..
[0030] The composition of the invention may further optionally
comprise one or more conventional additives in effective amounts.
Examples of suitable additives comprise UV absorbers; light
stabilizers such as benzotriazoles or oxalanilides; free-radical
scavengers; crosslinking catalysts such as dibutyltin dilaurate or
lithium decanoate; slip additives; polymerization inhibitors;
defoamers; emulsifiers, especially nonionic emulsifiers such as
alkoxylated alkanols and polyols, phenols and alkylphenols or
anionic emulsifiers such as alkali metal salts or ammonium salts of
alkane carboxylic acids, alkanesulfonic acids, or sulfo acids of
alkoxylated alkanols or polyols, phenols or alkylphenols; wetting
agents such as siloxanes, fluorine compounds, carboxylic
monoesters, phosphoric esters, polyacrylic acids or their
copolymers, polyurethanes or acrylate copolymers, which are
available commercially under the tradename MODAFLOW.RTM. or
DISPERLON.RTM.; adhesion promoters such as
tricyclodecane-dimethanol; leveling agents; film-forming
auxiliaries such as cellulose derivatives; flame retardants; sag
control agents such as ureas, modified ureas and/or silicas,
rheology control additives, such as those known from the patents
WO94/22968, EP0276501A1, EP0249201A1, and WO97/12945; crosslinked
polymeric microparticles, as disclosed for example in EP0008127A1;
inorganic phyllosilicates such as aluminum magnesium silicates,
sodium magnesium phyllosilicates or sodium magnesium fluorine
lithium phyllosilicates of the montmorillonite type; silicas such
as AEROSILS.RTM. silicas; or synthetic polymers comprising ionic
and/or associative groups such as polyvinyl alcohol,
poly(meth)acrylamide, poly(meth)acrylic acid, polyvinylpyrrolidone,
styrene-maleic anhydride or ethylene-maleic anhydride copolymers or
their derivatives or hydrophobically modified ethoxylated urethanes
or polyacrylates; flatting agents such as magnesium stearate;
and/or precursors of organically modified ceramic materials such as
hydrolyzable organometallic compounds, especially of silicon and
aluminum. Mixtures of such additives are also suitable in
particular embodiments.
[0031] The method of preparing the composition of the invention may
generally be carried out using conventional mixing of the
above-described components in appropriate mixing equipment, such
as, but not limited to, stirred tanks, dissolvers, homogenizers,
pressure release homogenizers, inline dissolvers, toothed-wheel
dispersers, microfluidizers, stirred mills, extruders, or like
equipment. It will be appreciated that appropriate measures to
minimize premature curing are typically employed. When compositions
in embodiments of the invention are employed to prepare composite
or laminate articles, the compositions may be combined with core
material, layer materials, or the like using known methods. In a
particular embodiment such articles are made using a resin infusion
method.
[0032] In a typical embodiment the composition is available as a
viscous gel or a liquid. The composition may be at least partially
cured by exposing to radiation having a wavelength in the range of
from about 200 nanometers to about 1000 nanometers, for example.
Suitable sources of such radiation may include, but are not limited
to, mercury arcs, carbon arcs, low pressure mercury arcs, medium
pressure mercury arcs, medium pressure mercury lamps, high pressure
mercury lamps, swirling flow plasma arcs, ultraviolet light
emitting diodes, ultraviolet light emitting lasers, and the like.
In particular embodiments the composition may advantageously be at
least partially cured or completely cured in the bulk state without
the use of any external solvents or diluents.
[0033] Upon exposure to radiation, the photoinitiator dissociates
to give rise to free radicals or acid, which then initiate the
curing of the photocurable monomer. The photocuring step is an
exothermic reaction and involves evolution of heat, which results
in an increase in temperature. Depending on the choice of the
curable monomer or combinations of curable monomers, and other
known factors, the extent of temperature rise may be controlled.
The increase in the temperature (sometimes referred to as an
exotherm) results in the dissociation of the thermal initiator to
give rise to free radicals, or acid, or other species effecting
curing. The free radicals or acid generated from the thermal
initiator will further initiate curing of the thermally curable
monomer, which will generate additional heat through exothermic
reaction and continue to propagate the cure through the thickness
of the composition. Thus, the composition is cured by thermal
curing as well as photocuring methods. Unless the type of curing is
specified, the terms "cured", "curing", and "curing step", as used
herein, comprise both photocuring and thermal curing steps. This
typically results in solidifying or at least partially solidifying
of the curable composition. The composition may be partially cured
or may be completely cured, to obtain a solid cured composition
having sufficient strength for the application being targeted.
Partial curing is said to have occurred when one or both of the
photocuring or thermal curing steps are at least partially
completed.
[0034] The time of exposure of the composition to radiation and the
intensity of the radiation may vary greatly. In various embodiments
the time of exposure to radiation or the intensity of the radiation
or both are sufficient to provide an exotherm sufficient to
initiate thermal curing. In particular embodiments the time of
exposure is generally in the range of from about 1 second to about
5 hours, more preferably in the range of from about 5 seconds to
about 1 hour. These parameters may be readily determined by one
skilled in the art. In one embodiment variations in the intensity
of radiation and time of exposure of the composition may be
employed to control the time taken to initiate thermal curing,
giving rise to "cure on demand" compositions.
[0035] In some embodiments the composition is exposed to the
radiation for a time period just sufficient to provide an exotherm
sufficient to initiate thermal curing, following which the
radiation source is turned off, and complete curing is achieved by
thermal curing. Subsequent to turning off the radiation source,
only thermal curing occurs. No other outside energy source is
employed to complete the curing of the composition after the
radiation source is turned off. In particular embodiments the
composition is exposed to the radiation for a time period
sufficient to provide an exotherm sufficient to complete the curing
of the composition by thermal curing. In other particular
embodiments the radiation source is turned off either before or
after or at the point at which the exotherm peak is achieved. In
particular embodiments the radiation source is turned off before
complete curing of the resin is achieved. This results in
significant reduction in energy usage, thus giving rise to a cost
effective process.
[0036] In other embodiments compositions of the invention can be
blended with at least one additional resin formulation, which can
be cured thermally such that the exotherm generated from the
compositions of the invention upon partial photocuring can be used
to initiate the onset of the thermal curing process which then goes
to completion without the application of an external heat source
and after the radiation source applied for photocuring has been
turned off. Illustrative additional resin formulations comprise
epoxy resins in the presence of a hardener.
[0037] Embodiments of the method described herein have been used
advantageously to cure compositions to form thick structures,
without the use of any external heat source, such as an oven, an
infrared heating lamp, a heating blanket or like heat source, by
utilizing the exothermic nature of the photocuring system, and thus
inducing thermal initiation and curing in sections where radiation
of the photocuring step cannot penetrate. This method also results
in efficient and uniform curing in all portions of the structure
being formed. The described method typically results in significant
time, energy and cost savings, among other advantages.
[0038] In another embodiment the method described herein has been
used advantageously to provide sandwich structures comprising a
reinforcing filler core sandwiched between composite laminate
(sometimes referred to as skin), wherein the skin comprises a dual
cure composition of the invention. Typically the core itself is
light weight, and the composite sandwich structure overall is a
light weight structure with very high bending stiffness. The core
material generally has a density less than 80% of the composite
skin density and more preferably less than 50% of the composite
skin density. Non-limiting examples of the core material comprise
wood, honeycomb, foam, slitted foam, and the like. Foam core may be
made from thermosets or thermoplastics. Typically the core material
is UV opaque. In many embodiments the core material has resin
pathways through the core to enable transfer of heat and free
radicals to propagate the cure through the full thickness. A
representative sandwich structure is shown in FIG. 3 wherein resin
filled spaces are depicted as vertical lines through the core of
the sandwich structure, the vertical lines corresponding to the
said resin pathways.
[0039] The composition and the methods described may be
advantageously used to make shaped components and articles. The
method is especially useful to make components and articles having
thicknesses greater than about 0.1 millimeters in some embodiments,
greater than about 0.5 millimeters in other embodiments, and
greater than about 1 centimeter in other embodiments. Illustrative
shaped components and articles comprise automotive components such
as body panels, truck beds, protective plates, fenders, spoilers,
hoods, doors or lamp reflectors; sanitary articles and household
implements; components for buildings, both inside and outside such
as doors, windows, and furniture; industrial components, including
coils, containers, and radiators; and electrical components,
including wound articles, such as coils of electric motors; wind
rotor blades for wind turbines; aerospace articles, bridge
components, marine articles, sporting goods, pipes, missiles, and
the like. Preferred shaped components and articles may also be made
of SMC (sheet molded compound) or BMC (bulk molded compound) as the
dual cure composition.
[0040] The composition and the methods described may be
advantageously used in composite repair in aerospace composites,
marine composites, automotive composites, composite tanks,
composite pipes, and the like. Dual cure resin compositions also
provide benefits of rapid cure for in service repair of thick,
highly filled composites or sandwich structures using EHS friendly
energy sources such as UV. Dual cure resin compositions minimize
issues with thermal management issues required with purely thermal
cure resins since a separate, external heat source is not needed to
initiate cure, and heat is generated within the resin itself.
[0041] Without further elaboration, it is believed that one skilled
in the art can, using the description herein, utilize the present
invention to its fullest extent. The following examples are
included to provide additional guidance to those skilled in the art
in practicing the claimed invention. The examples provided are
merely representative of the work that contributes to the teaching
of the present application. Accordingly, these examples are not
intended to limit the invention, as defined in the appended claims,
in any manner. In the following examples and comparative examples
the curable monomer was DION.RTM. 9800-05 urethane-modified vinyl
ester resin obtained from Reichhold Chemical Company, Durham, N.C.
Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (also referred to
hereinafter as "phosphine oxide") was IRGACURE.RTM. 819 obtained
from Ciba Specialty Chemicals, Tarrytown, N.Y., USA.
3,4-Epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, a
cycloaliphatic diepoxide (also referred to hereinafter as
UVACURE.RTM. 1500), was obtained from Cytec Surface Specialties.
Phenyl-p-octyloxyphenyl-iodonium hexafluoroantimonate, (also
referred to hereinafter as UVACURE.RTM. 1600), was obtained from
Cytec Surface Specialties. The epoxy laminating resin was type
L135i having an epoxy equivalent of 166-185 obtained from MGS
Kunstharzprodukte Gmbh, Stuttgart, Germany. Amine hardener was
H134i/H137i with an average amine equivalent of 52 obtained from
MGS Kunstharzprodukte Gmbh, Stuttgart, Germany. Methyl ethyl ketone
peroxide, NOROX.RTM. MEKP-9H was obtained from Norac, Azusa,
Calif., USA. Cobalt naphthenate, dimethyl aniline, and
2,4-pentanedione were obtained from Aldrich. The glass fiber fabric
was obtained from Saertex, Moorsville, N.C., USA. Carbon fiber
fabric was obtained from Sigmatex, Benicia, Calif., USA.
[0042] Interlaminar shear strength (ILSS) was determined by ASTM
D2344. Samples were prepared from 30 centimeter (cm).times.30 cm
panels with 24 plies of 1000 grams per square meter (gsm)+/45 biax
glass fabrics via a vacuum infusion process. Test specimen
dimensions were length.times.width.times.thickness=10 cm.times.1.9
cm.times.1.7 cm and the span length (S) was 6.6 cm with a span
ratio (S/T) of 4.
EXAMPLE 1
[0043] A formulation comprising DION.RTM. 9800-05 vinyl ester
resin, 1.2% MEKP, 0.2% cobalt naphthenate, 0.1% dimethyl aniline,
and 1% IRGACURE.RTM. 819 photoinitiator placed between glass plates
was cured by exposure to 400W UV-A portable arc lamp for 5 minutes,
after which the UV lamp was turned off. A glass laminate was
obtained that was 3.2 millimeters (mm) thick.
[0044] The resin formulations (abbreviated "Form.") used in
additional examples are shown in Table 1. Component amounts are
reported in parts by weight. TABLE-US-00001 TABLE 1 Form. Form.
Form. Form. Form. Component (I) (II) (III) (IV) (V) Curable monomer
100 100 100 0 0 Phosphine oxide 1 0 1 0 0 MEKP-9H 1.2 1.2 0 0 0 Co
naphthenate 0.2 0.2 0 0 0 Dimethyl aniline 0.1 0.1 0 0 0
2,4-pentanedione 0.2 0.2 0 0 0 UVACURE .RTM. 1500 0 0 0 100 0
UVACURE .RTM. 1600 0 0 0 1 0 Epoxy laminating 0 0 0 0 100 resin
Amine hardener 0 0 0 0 35
EXAMPLE 2
[0045] Two glass jars (each 5 centimeters diameter.times.4.4
centimeters height) were separately filled with 70 gm of
formulation (I) in Table 1. A thermocouple was placed in the center
of each glass jar to measure temperature rise with time. After 35
minutes, the radiation source UV-A 400W was turned on to illuminate
one of the jars for 15 minutes, after which it was turned off. The
temperature increased quickly and reached a peak value of
202.degree. C. As a comparative example, the same formulation (I)
was allowed to cure in the second jar without any UV radiation. The
temperature in the second jar did not begin to increase until 300
minutes and the temperature finally reached 136.6.degree. C. peak
temperature at 330 minutes. FIG. 1 shows the temperature profile at
the center of the formulation of each jar as determined by the
thermocouples. This demonstrated that the formulation and method of
the invention can achieve the cure on demand upon UV radiation
exposure at any time between time zero and 300 minutes in this
example.
EXAMPLE 3 AND COMPARATIVE EXAMPLE 1
[0046] A glass laminate with 24 plies of 1000 gsm +/-45 biax
fabrics was prepared from a composition comprising formulation (I)
via a resin infusion process for 25 minutes followed by photocuring
by exposure to 400W UV-A for 15 minutes, after which the UV lamp
was turned off. FIG. 2 shows the temperature profile at the center
of the formulation as determined by an embedded thermocouple. The
center temperature reached the maximum temperature of 67.degree. C.
in 15 minutes after UV light was shut off. The resin fully
solidified after debagging in 60 minutes from the start of 15
minute UV curing step to give rise to a 24 ply 15.9 mm thick glass
composite panel. The glass composite laminates produced in this
example had the same interlaminar strength properties as the glass
fiber composite laminates produced using formulation (II) with a
traditional cure schedule of room temperature cure for 4 hours and
followed by thermally postcure at 70.degree. C. for 10 hours.
Hence, the dual cure formulation (I) using an initial UV cure
attained the same product properties with significantly reduced
cure time and energy.
EXAMPLE 4
[0047] Carbon Fiber Composite Samples: A carbon fiber composite
formed by using a 5 cm.times.10 cm carbon fiber fabric
(TORAYCA.RTM. T700SC-12K-50C, 400 grams) comprising 3 plies formed
by hand lay-up and wet laminated with formulation (I). The
formulation was cured by exposure to UV radiation from a 400W UV-A
lamp for 10 minutes, after which the UV lamp was turned off. The
cured thickness was found to be 2.5 mm and was found to have
solidified throughout the sample. This example demonstrates the
dual cure composition overcomes the limitation of the UV light
penetration through carbon fiber composites.
COMPARATIVE EXAMPLE 2
[0048] A carbon fiber composite formed by using a 5 cm.times.10 cm
carbon fiber fabric (TORAYCA.RTM. T700SC-12K-50C, 400 grams)
comprising 3 plies formed by hand lay-up and wet laminated with
formulation (III) exposure to UV radiation from a 400W UV-A lamp
for 10 minutes, after which the UV lamp was turned off. Only the
top surface of the composite was cured and tack-free, while the
bottom remained a liquid and uncured. This comparative example
illustrates the necessity of a thermal initiator in addition to a
photoinitiator to attain thorough cure of carbon fiber composites
upon UV exposure.
EXAMPLE 5
[0049] Foam core wrapped samples: Glass wet laminate (wet hand
lay-up laminate of 1000 grams biax glass fabric) that was saturated
with formulation (I) was wrapped around a foam core having the
dimensions width.times.length.times.thickness=2.5 cm.times.11.4
cm.times.0.64 cm. This laminate was then cured by exposure to UV-A
radiation from a 400W UV-A lamp for 10 minutes, after which the UV
lamp was turned off. Ten minutes after shutting off the lamp, the
bottom layer of laminate was cured to solid. Cured laminated
thickness was found to be 1 mm.
EXAMPLE 6
[0050] Thick glass laminate: A 5 cm.times.7.5 cm wet laminate was
prepared from a 1000 grams biax glass fabric saturated with
formulation (I). The laminate was then built up to 3.2 cm thick by
the hand lay-up method. The laminate was then cured by exposure to
UV-A radiation from a 400W UV-A lamp. After 15 minutes, the UV
radiation was shut off. The temperature at the bottom of the
laminate (as measured with an IR pyrometer) was found to have
increased from 23.degree. C. to 100.degree. C. The laminate block
had completely solidified 5 minutes after the UV lamp was shut
off.
EXAMPLE 7
[0051] A carbon fiber composite formed by using a 5 cm.times.10 cm
carbon fiber fabric (TORAYCA.RTM. T700SC-12K-50C, 400 grams)
comprising 10 plies formed by hand lay-up and wet laminated with a
resin formulation that was a 50/50 (w/w) blend of formulation (I)
and formulation (IV). The composition was cured by exposure to UV
radiation from a 400W UV-A lamp for 14 minutes after which time the
UV lamp was turned off, and the temperature at the bottom of the
laminate had reached 170.9.degree. C. from 23.degree. C. indicating
significant heat exotherm had been generated due to the curing. The
sample was examined 5 minutes after turning off the UV lamp. The
composite of 6.35 mm thickness was found to have solidified
throughout the sample indicating complete curing. This example
demonstrates that both free radical and cationic curing mechanisms
are applicable in this invention and can be used in combination for
dual cure formulations.
EXAMPLE 8
[0052] A thick carbon fiber composite of 2.54 cm was formed by hand
lay-up using a 5 cm.times.10 cm carbon fiber fabric (TORAYCA.RTM.
T700SC-12K-50C, 400 grams) and wet laminated with a resin
formulation that was a 50/50 (w/w) blend of formulation (I) and
formulation (IV). The formulation was cured by exposure to UV
radiation from a 400W UV-A lamp for 43 minutes, after which the UV
lamp was turned off. The temperature at the bottom of the laminate
has reached 182.degree. C. from 23.degree. C. indicating
significant heat exotherm had been generated due to the curing. The
sample was examined 5 minutes after turning off the UV lamp. The
thick cured carbon composite of 2.54 cm was found to have
solidified throughout the sample. The example demonstrates that a
thick carbon fiber composite can be cured via UV exposure using the
formulations and method of the invention.
EXAMPLE 9
[0053] A carbon fiber composite of 6.35 mm formed by hand lay-up
using a 5 cm.times.10 cm carbon fiber fabric (TORAYCA.RTM.
T700SC-12K-50C, 400 grams) and wet laminated with a resin
formulation that was a 50/50 (w/w) blend of formulation (II) and
formulation (IV). The formulation was cured by exposure to UV
radiation from a 400W UV-A lamp for 20 minutes, after which time
the UV lamp was turned off. The temperature at the bottom of the
laminate had reached 192.degree. C. from 23.degree. C. indicating
significant heat exotherm had been generated due to the curing. The
sample was examined 5 minutes after turning off the UV lamp. The
cured carbon composite was found to have solidified throughout the
sample. This example demonstrates that a cationic UV curing from
cycloaliphatic epoxy can provide heat exotherm to decompose the
thermal initiator for free radical curing of the vinyl ester
resins.
EXAMPLE 10
[0054] A carbon fiber composite of 6.35 mm formed by hand lay-up
using a 5 cm.times.10 cm carbon fiber fabric (TORAYCA.RTM.
T700SC-12K-50C, 400 grams) and wet laminated with a resin
formulation that is a 50/50 (w/w) blend of formulation (I) and
formulation (V). The formulation was cured by exposure to UV
radiation from a 400W UV-A lamp for 32 minutes, after which time
the UV lamp was turned off. The temperature at the bottom of the
laminate had reached 140.degree. C. from 23.degree. C. indicating
significant heat exotherm has been generated due to the curing. The
sample was examined 5 minutes after turning off the UV lamp. The
cured carbon composite was found to have solidified throughout the
sample. This example demonstrates that the dual cure formulation
upon UV exposure can provide heat exotherm to activate the thermal
curing of an amine/epoxy resin system.
[0055] The examples demonstrate that formulations comprising a
combination of a photoinitiator and a thermal initiator are capable
of forming cured compositions such as, but not limited to, carbon
fiber composites and composites with foam core and thick section
composites, without separate external application of heat as
compared to the comparative example, wherein complete curing could
not be achieved in the absence of the thermal initiator and without
the separate external application of heat. The examples also
demonstrate that the method is applicable to a wide variety of
formulations, irrespective of whether the fillers used are UV
opaque or UV transparent.
[0056] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
* * * * *