Note: Descriptions are shown in the official language in which they were submitted.
~ 80 RD-10108
The present invention relates to UV curable
compositions and a method of curing, based on the
simultaneous generation of free-radicals and a cationic
curing catalyst. More particularly, the present invention
relates to the use of a triarylsulfonium salt as a
photoinitiator for the simultaneous free-radical and
cationic cure of oxirane containing aliphatically
unsaturated organic materials.
In U.S. patents 4,058,400 and 4,058,401 both
issued November 15, 1977 to James V. Crivello and
assigned to the present assignee, there is described the
use of triarylsulfonium salts of the formula
(1) [(R)3S] [MQd]
where R is a monovalent aromatic organic radical, M is
a metal or a metalloid, Q is a halogen selected from F and Cl,
and d is an integer having a value of from 4 to 6 inclusive,
as initiators to effect the polymerization of various
cationically polymerizable organic materials. In
Canadian patent application Serial Number 310,436
filed August 31, 1978 in the names James V. Crivello
and James E. Moore, titled "Photocurable Compositions and
Method for Curing" and assigned to the present assignee,
there is described the use of triarylsulfonium salts of
formula (1) as a free radical photoinitiatorfor aliphatically
unsaturated organic resins, e.g. acrylic resins and certain
. ' - 1 -
~ 180 RD-10108
unsaturated polyester mixtures which are free of oxirane
oxygen. In U.S. patent No. 3,028,361 dated April 3, 1962
Abrams et al, there is described the use of sulfonium salts
as stabilizers for free radical polymerizable compositions,
such as a polyester monomer composition. Based on the
teaching of Abrams et al, the cure of the aforementioned
polyester composition can be effected by the employment of
a free-radical initiator, such as a peroxide catalyst, for
example, benzoyl peroxide. Although the cure of such
10 aliphatically unsaturated organic materials, either by
way of free radicals, or by a cationic mechanism, improves
the utility of starting aliphatically unsaturated organic
material, coatings of such materials on various substrates
often do not have the solvent resistance needed in particular
applications. It would be desirable therefore to develop
a technique whereby organic coatings formed by the cure of
applied aliphatically unsaturated materails can be made in
an improved manner to achieve characteristics not obtainable
by techniques known to the art.
The present invention is based on the discovery that
oxirane containing aliphatically unsaturated organic materials
can be cured by a simultaneous free-radical and cationic
mechanism, whereby improved characteristics are obtained in
the final product, such as solvent resistance. Simultaneous
free-radical and cationic cure of oxirane containing aliphatic-
ally unsaturated organic materials can be achieved in accord-
ance with the practice of the present invention by the use
of an effective amount of triarylsulfonium salts of formula
(1) in such oxirane containing aliphatically unsaturated
organic materials and the exposure of such photocurable
compositions to radiant energy and preferably ultraviolet
light.
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RD-10108
There is provided by the present invention, photo-
curable compositions comprising
(A) oxirane containing aliphatically unsaturated
organic material and
(B) 0.1 to 15% by weight of (A)of a triarylculfon-
ium salt of formula (1).
Radicals included by R of formula (1) are, for
example, C(6_13) aromatic hydrocarbon radicals, such as phenyl,
tolyl, naphthyl, xylyll anthryl, etc. Radicals included by
M of formula (1) are metal or metalloids, such as a transition
metal, for example Sb, Fe, Sn, Bi, Al, Ga, In, Ti, Zr, Sc, V,
Cr, Mn, Cs, rare earth elements such as the lanthanides, for
example, Ce, Pr, Nd, etc., actinides, such as Th, Pa, U, Np,
etc., and metalloids such as B, P, As, etc.
Triarylsulfonium salts included by formula (1) are,
for example,
( ~ +S ~ )2
Cl 3 SbF6
3 PF
6 ~ BF~
~ ~ AsF6 ~ i AsF6
C(CH3)3 Cl
~l Z~ ~80 RD-10108
Triphenylsulfonium qalts included in formula ~1) can
be made by procedures shown in J.W. Knapczyk and W.E. McEwen,
J. Am. Chem. Soc., 91 145, (1969); A.L. Maycock and G.A.
Berchtold, J. Org. Chem. Soc. 35, No. 8, 2532 (1970); H.M.
Pitt, U.S. patent 2,807,648, E. Goethals and P. De Radzetzky,
Bul. Soc. Chim. Belg., 73 546 (1964); J.M. Leicester and
F.W. Bergstrom, J. Am. Chem. Soc., 51 (1929), etc.
A free radical cure can be achieved also with the
triarylsulfonium salts of formula (1) with oxirane containing
aliphatically unsaturated polyester resins having chemically
combined oxirane oxygen in combination with vinyl aromatic
compounds or mixtures of such resins with or without chemically
combined oxirane oxygen with compounds such as glycidyl
acrylate, glycidyl methacrylate, bisphenol-A-diglycidyl ethers,
4-vinylcyclohexane dioxide, 3,4-epoxycyclohexyl-3',4'-epoxy-
cyclohexane carboxylate, diglycidyl phthalate, cyclohexene
oxide, 1,4-butanediol diglycidyl ether, C4-C30 ~-olefin oxides,
epoxy-novolac resins, such as DEN 431, DEN 438, DEN M 439,
manufactured by the Dow Chemical Company of Midland, Michigan,
etc.
In addition to the above compounds, oxirane containing
polymeric materials containing terminal or pendant epoxy groups
also can be blended with acrylic resins or with the unsaturated
polyester compositions described above. Examples of such
oxirane containing polymeric materials are vinyl copolymers
containing glycidyl acrylate or methacrylate as one of the
comonomers. Other classes of epoxy containing polymers
amenable to free radical cure using the above tri-
arylsulfonium catalysts of formula (1) are epoxy-siloxane
resins, epoxy-polyurethanes and epoxy-polyesters. Such
polymers usually have epoxy functional groups at the ends of
their chains. Epoxy siloxane resins and method for making are
llS~U~80
RD-10108
more particularly shown by E.P. Plueddemann and G. Fanger, J,
Am. Chem. Soc. 81 632-5 (1959). As described in the literature,
epoxy resins can also be modified in a number of standard ways,
such as reaction with amines, carboxylic acids, thiols, phenols,
alcohols, etc., as shown in U.S. Patents 2,935,488; 3,235,620;
3,369,055; 3,379,653; 3,398,211; 3,403,199; 3,563,850; 3,567,797;
3,677,995; etc. Further examples of epoxy resins which can be
used are shown in the Encyclopedia of Polymer Science and
Technology, Vol. 6, 1976, Interscience Publishers, New York,
pp 209-271.
There can be included with the above-described organic
resins, 100 parts of fillers per 100 parts of organic resins
and other materials such as flatting agents, thixotropic agents,
dyes and pigments such as barytes, blanc fixe, gypsum, calcium
carbonate, quartz, diatomaceous silica, synthetic silica, clay
talc, asbestos, mica, bentonite, aerogels, glass fibers, basic
carbonate, white lead, antimony oxide, lithophone, titanium
dioxide, ultramarine blue, aluminum powder, etc.
Cure of the photocurable compositions of the present
invention can be achieved by either heating the composition at
a ~mperature in the range of from 150C to 250C or by use of
radiant energy, such as electron beam or ultraviolet light.
Electron beam cure can be effected at an accelerator voltage
of from about 100 to 1,000 Kv. Cure of the compositions is
preferably achieved by the use of UV irradiation having a wave-
length of from 1849 A to 4000 A and an intensity of at least
5,000-80,000 microwatts per cm2. The lamp system used to gener-
ate such radiation can consist of ultraviolet lamps such as from
1 to 50 discharge lamps, for example, xenon, metallic halide,
metallic arc, such as a low, medium or high pressure mercury
ll~U180
RD-10108
vapor dischargelamp~ etc., having an operating pressure of from
a few millimeters to about 10 atmospheres, etc., can be employed.
The lamps c~n include envelopes capable of transmitting light
of a wavelength of from about 1849 A to 4000 A, and preferably
2400 A to 4000 A. The lamp envelope can consist of quartz,
such as Spectroc l, or Pyrex, etc. Typical lamps which can be
employed for providing ultraviolet radiation are, for example,
medium pressure mercury arcs, such as the GE H3T7 arc and the
~ Hanovia 450 W arc lamp. The cures may be carried out with a
combination of various lamps, some or all of which can operate
in an inert atmosphere. When using W lamps, the irradiation
flux on the ubstrate can be at least 0.01 watts per square
inch to effect cure of the organic resin within 1 to 20 seconds
and permit the cure to be carried on continuously.
In order that those skilled in the art will be better
able to practice the invention, the following examples are
given by way of illustration and not by way of limitation.
All parts are by weight.
~Exa~ple 1.
Two solutions were prepared. The first solution
consisted of glycidylacrylate containing 1% by weight of tri-
phenylsulfonium chloride as a photoinitiator. The second
solution consisted of glycidyl acrylate with 1~ triphenylsul-
fonium hexafluoroantimonate.
Both solutions were spread to a thickness of 1 mil on
steel plates and irradiated for 30 seconds at a distance of
four inches from a G.E. H3T7 medium pressure mercury arc lamp.
The coatings of both the samples were dry and hard.
Both samples were then immersed into methylethyl
ketone. The sample cured with triphenylsulfonium chloride as
0~80
RD-lOlOB
the catalyst was removed after 1 minute, whereas the sample
using triphenylsulfonium hexafluorophosphate was unaffected
after 15 minutes immersion.
The above results demonstrate the superior solvent
resistance of cured films based on the use of triphenylsulfon-
ium hexafluoroantimonate, which is capable of initiating a
simultaneous free-radical and cationic cure.
Example 2.
A blend of 66% by weight of an aliphatically unsatur-
ated polyester in the form of a reaction product of isophthalic
acid, fumaric acid and diethyleneglycol and 34% by weight of
styrene and about 2% by weight of the blend of triphenylsul-
fonium hexafluoroarsenate was coated onto a steel panel and
cured for 1 minute using a G.E. H3T7 medium pressure mercury
arc lamp. The same procedure was repeated, except that in
place of the aforementioned blend (A), there was used a blend
of 33% by weight of aliphatically unsaturated polyester, 17%
by weight of styrene and 50~ by weight of a bisphenol-A-digly-
cidyl ether (Shell Epon 828). The latter blend (B) containing
2% by weight of the triphenylsulfonium hexafluoroarsenate was
also applied onto a steel panel and irradiated following the
same procedure.
The above 2 panels were immersed in a 50% aqueous
sodium hydroxide solution. After one hour at 95C, blend (A)
free of oxirane oxygen was found to be completely degraded.
However, blend (B) which contained the epoxy resin was found
to be substantially unchanged. These results indicate that
the simultaneous cure provided by the method and compositions
of the present invention result in cured products having super-
ior hydrolysis resistance. ~Iydrolysis degradation also occurred
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l~Z0~80
RD-10108
when benzoin butyl ether was substituted for tlle triphenyl-
;,
sulonium salt as a free-radical initiator in blend (A).
Example 3.
A photocurable composition (C) was prepared by mix-
ing together 98 parts of trimethylolpropane triacrylate and
2 parts of benzoin butyl ether. Composition (D) was
prepared by blending together 98 parts of trimethylolpropane
triacrylate and 2 parts of triphenylsulfonium hexafluoroanti-
monate. There was also blended together (E) 49 parts of tri-
methylolpropane triacrylate, 49 parts of bisphenol-A diglycidyl
ether and 2 parts of triphenylsulfonium hexafluoroantimonate.
The above 3 photocurable mixtures were respectively
coated to a thickness of about 2 mil onto steel panels. The
respective steel panels were then cured in accordance with the
procedure of Example 1. It was found that blends (C) and (D)
required 5 minutes cure to produce a tack-free film, while
blend (E) was cured within 30 seconds irradiatio~. The three
coated steel panels were then respectively immersed in a 50%
aqueous sodium hydroxide solution at 95C. It was found that
after 30 minutes the coatings from blends (C) and (D~ were
removed by hydrolysis, while the coating obtained from the
cure of blend (E) remained su~stantially intact.
The above results establish that the simultaneous
free-radical and cationic cure achieved in accordance with the
practice of the invention provides superior results with respect
to cure time and ability to resist alkaline hydrolysis at
elevated temperatures.
Example 4.
A series of photocurable blends were prepared employ-
ing 2% by weight of the blend of triphenylsulfonium hexafluoro-
l~ZOl~10
RD-10108
antimonate as the ~otoinitiator. The first blend consisted
of lauryl acrylate and the second blend consisted of 3,4-epoxy
cyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate. Another
blend consisted of about 78~ by weight of the 3,4-epoxycyclohexyl-
methyl-3',4'-epoxycyclohexanecarboxylate and about 20% by weight
of lauryl acrylate. The above three blends were respectively
applied onto glass plates to a thickness of about 2 mil and
thereaftqr cured for 1 minute under ultraviolet radiation as
described above. The coated glass plates were then immersed
in water to effect the removal of the respective films which
were tack-free. The film made from the first blend was
found to be very soft and extremely fragile. The film made
from the second blend was hard, brittle and rigid and readily
broke when it was attempted to bend it to an angle of 45. The
film obtained from the third mixture was tough and flexible
and could be readily bent to 180 without breaking. ~hese
results establish that the simultaneous cure provided by the
photocurable mixture of the presen~ invention provides tough
flexible films which could not be obtained by the practice of
the procedures of the prior art.
Example 5.
A series of photocuxable mixtures were prepared con- -
taining about 3% by weight of triphenylsulfonium hexafluoro-
antimonate. Trimethylolpropane triacrylate was utilized in
all of the mixtures which was further blended in particular
instances with an oxirane containing material. The various
mixtures were then applied onto a glass substrate to a thick-
ness of 2 mils and exposed to a G.E. H3T7 lamp at a dis-
tance of about 8 inches to determine the period of time to
convert the photocurable composition to a cured tack-free film.
~l'h()180
RD-10108
The following results were obtained, where "TMT" i8 trimethylol-
propane triacrylate, "Initiator" is triphenylsulfonium hexa-
fluoroantimanate, "VCD" is 4-vinylcyclohexene dioxide and "EPON
828" is a bisphenol-A diglycidyl ether:
Mixture WT% Cure Time
TMT 97%
Initiator 3% 5 min.
TMT 87%
VCD 10% 3.5 Min.
Initiator 3%
TMT 73%
VCD 24% 30 sec.
Initiator 3%
TMT 73%
- EPON 828 24% 30 sec.
Initiator 3~
The above results show that mixtures of acrylate and
the triphenylsulfonium initiator containing a minor amount of
oxirane containing material can be cured in air in a relatively
short period of time. One possible explanation is that the
oxirane containing material eliminates the effect of oxygen
inhibition because the cationic polymerization precedes the
free-radical polymerization.
In addition to the triarylsulfonium salts of formula
(1), there also can be used in the photocurable compositions
of the present invention triarylsulfonium salts of the formula
(2) [(R)a (R )b S] [MQ
where R is selected from the group consisting of a C(6 13~
aromatic hydrocarbon radical and a heterocyclic radical and
substituted derivatives thereof, Rl is a divalent aromatic
hydrocarbon radical, a divalent heterocyclic radical and sub-
stituted derivatives thereof,
--10--
1~ ~0 ~ ~ RD-10108
a is an integer having a value of 1 or 3,
b is an integer having a value of 0 or 1,
and the sum of a + 2b is equal to 3, and
MQd is as previously defined.
Although the above examples are directed to only a
few of the very many variables which are included by the
photocurable compositions of the present invention and the method
of curing such compositions, it should be understood that a
much broader variety of photocurable compositions is encompassed
within the scope of the present invention, as shown by the
description preceding these examples.
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