Note: Descriptions are shown in the official language in which they were submitted.
q ~
RD-8618
PHOTOCURABLE COMPOSITIONS AND METHOD FOR CURING
The present invention relates to UV curable composi-
tions and a method of curing based on the generation of free-rad-
icals. More particularly, the present invention relates to the
use of a triarylsulfonium photoinitiator to effect the free-rad-
ical cure of acrylic resins and certain unsaturated polyester
mixtures.
Prior to the present invention, as taught by Passalenti
et al, U.S. patent 3,~16,366 and U.S. patent 3,627,657, free-rad-
ical photocurable mixtures such as unsaturated polyesters had to
be stabilized with materials, such as arylphosphites when using
photoinitiators such as benzoin and its derivatives. It has
been found, for example, that unless a stabilizer is employed
in such photoc:urable resin mixtures that the shelf life of such
materials is often less than 6 weeks under atmospheric condi-
tions. However, even with stabilizers, free-radical photocuring
organic resins often have shelf lives of less than 6-12 months
at ambient temperatures. As shown by Abrams et al, U.S. patent
3,028,361, sulfonium salts can be used as a stabilizer for
polyester compositions which are thermally cured with a peroxide
catalyst.
Improved shelf stability has been found for free-rad-
ical photocuring organic resin mixtures, as shown in Smith
patents 3,72g,313 and 3,808,006, when a complex catalyst system
is used. For example, Smith teaches that a diaryliodonium com-
pound can be used as photoinitiators in combination with a
sensitizing organic dye, such as acridine and a photolyzable
organic halogen compound, such as 2-methyl-4,6-bis(trichloro-
methyl)-s-triazine. It would be desirable therefore to effect
the free-r~dical cure of various resins such as acrylics and
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RD-8618
mixtures of aliphatically unsaturated polyesters and vinyl
aromatic organic compounds by employing a photoinitiator which
does not require the presence of a stabilizer or does not
; require theuse of a combination of additional ingredients, such
as the aforementioned organic dye and substituted triazine shown
in the aforesaid patents of Smith,while at the same time possess
a superior shelf life, such as greater than 6 months at ambient
temperatures.
The present invention is based on the discovery that
triarylsulfonium salts having the formula,
+
(1) [(R)3 S~ [Y~ ,
where R can be a monovalent C(6-13) aromatic radical and
Y is an anion, can be used as a photoinitiator to effect the
photocure of free-radical curable organic resins such as thiol-
ene resins, or acrylic resins, mixtures of aliphatically unsat-
urated polyesters with vinyl aromatic compounds, etc., in a
relatively short period of time, such as an exposure of from
; 0.5-l minute or less to ultraviolet light. In addition, it
has been found that such photocurable organic resin mixtures
possess superior shelf life for a period exceeding 6 months at
ambient temperatures in the absence of a phenolic or quinonic
inhibitor.
As taught in Canadian Application S.N. 306~523 of
J.V. Crivello, filed June 29, 1978 and assigned to the
same assignee as the present invention, Y of formula (1) can be
an M(Q)d radical, where M is a metal or metalloid, and Q is a
halogen radical and a has a value su~h as 4-6, for example AsF6.
If such M(Q)d triarylsulfonium salt is used in combination with
c c~
A a free-radical ~urca~ organic resin, such as an acrylic, or an
9~
RD-8618
aliphatically unsaturated polyester having cationic curing sites
such as oxirane oxygen, either in the form of a mixture with
an organic compound, such as epoxy monomer, for example, an
epoxy acrylate, or as a chemically combined unit, for example,
an oxirane unit in the backbone of the unsaturated polyester
and such photocurable mixture is irradiated, a simultaneous
free-radical and cationic cure of the organic resin can be
achieved.
There is provided by the present invention, photocur-
~ 10 able organic resin compositions comprising,
; (A) a free radical curable organic resin free of oxi-
rane oxygen selected from the class consisting of acrylic resins,
and thiol-ene resins, and
(b) from 0.1 to 15~ by weight of (A) and (B) of tri-
arylsulfonium salt of formula (1).
Additional photocurable compositions provided by the
present invention comprise
(C) free-radical curable organic resins having chem-
ically combined oxirane oxygen of the formula,
-C ~- -~ C- , and
; (D) from 0.1 to 15% by weight of (C) ~nd (D) of a tri- arylsulfonium salt of the formula,
~2) [(R)3 S ] [X]
: where R is as previously defined and X is an anion selected
from halogen, NO3, HSO4, and H2PO4.
Radicals included by R of formulas 1-2 are, for example,
C(6 13) aromatic hydrocarbon radicals such as phenyl, tolyl,
naphthyl, anthryl and such radicals substituted with up to 1 to
4 monovalent radicals such as C(l 8) alkyl, nitro, chloro,
~ 96 RD-8618
hydroxy, etc.; aromatic heterocyclic radicals such as pyridyl,
~urfuryl, etc. Anions included by Y of formula (1) are, for
example, halogen, for example, chlorine, bromine, fluorine and
iodine: NO2, E~SO3, ClO~ , etc; ilQd, such as BF4 ,PF6 , AsF6 ,
SbFh , FeC14 , SnCl , SbC15 , BiC15 , AlF~ , GaCl~ , InF4 , TiF6
ZrF6 , etc. Additional metals included b~ M are, for example,
transition metals such as Zr, Sc, V, Cr/ Mn, Cs, etc; rare qarth
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.
Triphenylsulfonium salts included in formulas (1) and
(2) can be made by procedures shown in J.W. Knapczyk and W.E.
McEwen, J. Am. Chem. Soc., 9o 145, (1969); A.L. Maycock and G.A.
Berchtold, J. Or. Chem. Soc. 35, No. 8, 2532 (1970); H.M. Pitt,
U.S. patent 2,807,648, E. Goethals and P. DeRadzetzky, Bul. Soc.
Chim. Belg., 73 546 ~1964); H.M. Leicester and F.W. Bergstrom,
J. Am. Chem. Soc., 51 3587 (1929), etc.
Some of the triphenylsulfonium salts included in
formula (1) are, for example,
20( ~ S+SbF ~ (Cl ~ S Br
S+A F ~ ( ~ S F2P4
/ CH
~ ~ S BF4 ( ~ S+NO3
CH3 3
9~
RD-8618
$ 3 ( ~ S Cl
CH3
Included within the triphenylsulfonium salts of
formula (2) are, for example,
( ~ S+Cl ( ~ S+~r
~ ~ ~ D ~
3 1 HS04 ~ etc.
where D can be 0, S, S=O, C=O ! O=s=O, R-N, etc.
Among the free-radical curable compositions which
: can be used in the practice of the present invention are ali-
phatically unsaturated polyesters which can be reaction products
of organic polycarboxylic acidsj such as phthalic, isophthalic,
adipic, glutaric, malonic, succinic, suberic, azelaic, tetra-
chlorophthalic, tetrahydrophthalic, chemically combined through
ester linkages with one or more aliphatically unsaturated poly-
carboxylic acid units, such as fumaric, maleic, citraconic, ita-
conic, which po~ycarboxylic acids are reacted with glycols, such
as 1,4-butanediol, 1,4-cyclohexanedimethanol, ethyleneglycol,
diethyleneglycol, triethyleneglycol, etc., 1,2-propyleneglycol,
isomers of dihydroxybenzene, bisphenols, such as 2,2-diphenyl-
11&~ 96
RD-3618
phenylol propane, halogenated bisphenols, etc. Experience
has shown that in order to provide for effective curing results,
there should be employed at least 5 mol percent to 5~ mol per-
cent of aliphatically unsaturated polycarboxylic acid units
based on the total moles of polycarboxylic acid units in the
polyesters. In addition, small quantities of monofunctional
and polyfunct:ional organic acids and glycols, such as palmitic
acid,pyromellitic acid, glycerin, cyclohexanol, etc., may also
be incorporated in the polyester to obtain specific desirable
properties. ~lthough the molecular weight of the unsaturated
polyesters can be in the range of from about 2,000 to 10,000,
it is preferred that the molecular weight be in the range of
from about 2,000 to 6,000. As preferred class of unsaturated
polyesters is a reaction product of fumaric acid, isophthalic
acid and propyleneglycol having aliphatic unsaturation within
the aforementioned definition.
Vinyl aromatic organic compounds which can be employed
in combination with the aliphatically unsaturated polyesters
include, for example, styrene, vinyltoluene and N-vinylpyrroli-
done. A proportion of the vinyl aromatic compound such as
styrene which can be used in combination with the unsaturated
polyesters can vary widely depending upon the degree of ùnsat-
uration inthe polyester as well as the viscosity of the mixture
desired. It has been found, for example, that effective results
can be achievecl if from 0.5 mols to 10 mols of the vinyl aromatic
compound are used permole of aliphatically unsaturated polycar-
boxylic acid units in thepolyester. In addition to the afore-
mentioned vinyl aromatic compounds, there also can be used in
combination with the aliphatically unsaturated polyester com-
pounds, such as methyl methacrylate, ethyl methacrylate, butyl-
11~6(~96
RD-8618
acrylate, butyl methacrylate, acrylonitrile, vinyl acetate, di-
ethyl ~umarate, dipropyl fumarate, diallylphthalate, etc. Furthe
small amounts of polyfunctional monomers such a8 1,3-butylene-
glycol diarylatej polyethyleneglycol diacrylate, ethyleneglycol
diarylate, etc., can be employed to enhance the cross-link dens-
ity of the cured polyester,
The acrylic resins which can be used to make the
photocurable compositions of the present invention include
polymers and copolymers derived from esters of acrylic and
J~
methacrylic acid, such as Acryloid polymers of the Rohm and
~Iaas Company or Elvacite resins of the DuPont Company.
Monomers shown by the above formulas which can be
utilized in combination with the above organic polymers are,
for example, esters of acrylic and methacrylic acids such as
methyl methacrylate, butyl methacrylate, butyl acrylate, ethyl
acrylate, hydroxyethyl acrylate, hydroxymethyl acrylamide,
methoxyethyl acrylate, 2-ethoxyethyl methacrylate, ethylhexyl
acrylate, hexadecyl acrylate or cyclohexyl acrylate. Small
amounts of vinyl esters or ethers, such as vinyl acetate, vinyl
propionate, or butyl vinyl ether, vinyl aromatics such as
styrene, vinyl toluene, tertiary butyl styrene, or p-chloro-
styrene, or other unsaturated monomers~ such as diethyl
fumerate, acrylonitrile, or N-vinyl-2-pyrrolidone or vinylidene
chloride may also be included.
Also included in the above are multifunctional acrylate
and methylacrylate monomers, such as neopentylglycol diacrylate,
hexanediol diacrylate, trimethylolpropane triacrylate, penta-
erythritol tetraacrylate, etc., or methacrylated oligomeric com-
positions, such as acrylate terminated polyesters and polyure-
thanes.
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.
)96
RD-8618
; In addition to the above described resins, the triaryl
sulfonium salts of formula (1), can be used in combination with
thiol-ene resins, some of which are shown by Kerr et al U.S. pat-
ents 3,697,3~5, 3,697,396, 3,697,402, 3,700,574 and 3,661,744.
A free radical cure also can be achieved with the tri-
arylsulfoniun~ salts of formula (2) with oxirane containing or
aliphatically unsaturated polyesters, having chemically combined
oxirane oxygen in combination with vinyl aromatic compounds, or
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'-epoxycyclohexane carboxylate, diglycidyl
phthalate, cyclohexene oxide, 1,4-butane diol diglycidyl ether,
C4-C30 ~-olefin oxides, epoxy-novolac resins, such as DEN 431,
DE~I 438, DEN 439, manufactured by the Dow Chemical Company of
Midland, ~chigan, etc.
In addition to the above compounds, oxirane containing
polymeric materials containing terminal or pendant epoxy groups
also can be blended with the acrylic resins or the unsaturated
polyester compositions described above. Examples of these
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 triaryl~,ulfonium catalysts of formula (2) are epoxy-silox-
ane resins, epoxy-polyurethanes and epoxy-polyesters. Such
polymers usua]ly have epoxy functional groups at the ends of
their chains. Epoxy siloxane resins and method for making are
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,
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~ ; RD 8618
alcohols, et:c., as shown in 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.
III instances where the triarylsulfonium salts of
formula (2) are used to effect the photocure of free-
radical polymerizable materials, it has been found
desirable to employ from 0 to 95 mole percent of cationic
functional groups and 5 to 100 mole percent of free radical
functional groups, based on the total moles of cationic
functional groups and free-radical functional groups in the
mixture. Free radical or cationic functionality can be
present in the mixture. Free radical or cationic function-
ality can be present in the mixture as part of a compound,
or as a polyvalen~ unit chemically combined without poly-
valent units as part of a polymer or copolymer.
As taught in Canadian applications of James V.
Crivello filed May 2, 1975 Serial Numbers 226,108; 226,107
and 226,109 assigned to the same assignee as the present
invention, cationic polymerizable materials are provided
comprising either epoxy resins or various vinyl organic
and cyclic organic compounds utilizing halonium salts and
onium salts of Group Va and VIa elements. More particularly,
there is included, triphenylsulfonium salts included by
formula (1) as a photoinitiator for epoxy resins, vinyl
organic compounds and cyclic compounds in Serial Number
226,108. However, in accordance with the above cited
teaching of Canadian Application Serial No. 306,523 of J. V.
11~ 96
RD-8618
Crivello, the simultaneous free radical and cationic photocure
of t~e mixtures utilized in the practice of theinvention, providc
for advantages significantly different from those provided by
both the present invention, as well as those shown in the afore-
mentioned Crivello applications.
There also aan be included in the free radical curable
compositions of the present invention,100 parts of filler, per
100 parts of organic resin 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, gla~s fibers, basic carbonate, white lead, anitmony
oxide, lithophone, titanium dioxide, ultramarine blue, aluminum
powder, etc.
; 15 Cure of the photocur~ble composition of the present
invention can be achieved by either heating the composition at
a temperature 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 systems used to
generate 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 vapor discharge lamp, etc., having an operating pres-
sure of from a few millimeters to about 10 atmospheres, etc.,
can be employed. The lamps can include envelopes capable of
transmitting light of a ~avelength of from about 1849 A to
4000 A, and preferably 2400 A to 4000 A. The lamp envelope
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RD-8618
can consist of quartz, such as Spectrocil, or Pyrex, etc.
Typical lamps which can be employed for providing ultraviolet
radiation are, for example, medium pressure mercury arcs, such
Ai as ~e 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.
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.
Example l.
A variety of free-radical curing compositions were
prepared using as photoinitiators, butylbenzoin ether (Triganol~
14) and triphenylsulfonium hexafluoroarsonate. The free-radical
~` 15 cureable organ:ic resin included a mixture of 33% by weight
` styrene,and 67% by weight of an aliphatically unsaturated poly-
ester in the form of a reaction product of isophthalic acid,
fumaric acid and diethyleneglycol. Another free-radical curable
organic resin consisted of equal parts by weight of methyl-
methacrylate and polymethylmethacrylate. A third free-radical
curable organic resin employed was trimethylol propane triacryl-
ate. The aforementioned photoinitiators were respectively
employed in each of the aforementioned free-radical curable
organic resins at 3% by weight. An additional series of photo-
curable resins were prepared employing equal molar amounts of
the triphenyl sulfonium hexafluoroarsonate and the Triganol 14
~ r~e~ /~la~ h~ -11-
11~6q'1~96
RD-8618
photoinitiator, manufactured by the Noury Chemical Company, with
the aforement:ioned free-radical curing organic resins.
The above photocurable mixtures were then respectively
applied onto steel strips to a thickness of about 2 mils and
the treated ~trips were passed through a curing oven utilizing
G.E. H3T7 medium pressure mercury arc lamps at a distance of
about 8 inches from the lamps. The following results show the
conveyer speed in feet per minute required to produce a tack-free
surface on the steel strip as it passed through the curing oven,
where "M" indicates moles of photoinitiator.
Conveyer Speed (ft/min)
For Tack-Free Surface
Resin Trlganol 6 5)3 ~SF6 6 5)3 ASF6
-- (0.0066M) (O.OllM)
33% Styrene 60 35-50 50
67% Polyester
50% Methylmeth-
acrylate
50~ Polymethyl- 75 50 50
methacrylate
Trimethylol-
propane 350 300 300
Triacryalte
The above results show that the triphenylsulfonium
salt was substantially equivalent to the Triganol 14 as a W
free-radical photoinitiator.
Example 2.
A series of blends of trimethylolpropane triacrylate
with various onium salts utilized at 1~ by weight, based on
the weight ~ the blend, were prepared. The blends were
applied on to glass plates to a thickness of 1.5 mil and
irradiated at a distance of 6 inches from a G.E. H3T7 lamp
6~
RD-8618
to determine whether the particular onium salt used was capable
of initiating a free radical cure. The following results w~re
obtained, where "Yes" indicates that a tack-free film was
obtained, "No" indicates that the blend remained uncured and
"Cure Time" indicates length of exposure under the H3T7 lamp.
Onium Salt Cure Time (sec) Cure
_ _
(C6H5)3S ASF6 15 Yes
(C6H5)3S sbF6 15 Ye~
( 6 5)3 6 15 Yes
~CH ~ S BF4 15 Yes
~(CH3)3c ~ 2I AsF6 15 No
" 30 No
¦(CH3)2CH ~ I AsF6 120 No
~(CH3)3c ~ I Br 60 No
. O
~C-CH2-S ~ 6 30 No
CH30
H~ +~CH3 60 No
CH30
C-CH2-N ~ AsF6- 60 No
O +
C-CH2-P(C6H5~3sF4 60 No
~ C6H5
C6H5-CH2- ~ BF4 60 No
-13-
RD-8618
The above results show that the triarylsulfonium
salt of the present invention must be employed to effect the
free-radical polymerization. No cure was obtained when diphenyl-
benzylsulfonium fluoroborate was utilized because the methylene
radical apparently interfered with the results achieved by the
practice of the present invention.
Example 3.
A 1% solution of triphenylsulfonium hexafluorophos-
; phate in hydroxypropylacrylate was irradiated in accordance with
the procedure of Example 2. It was found that a polymer was
obtained ~sed on a 98% conversion of the monomer in less than
1 minute.
Example 4.
There was added 0.15 part (3%) by weight of triphenyl-
sulfonium chloride to 5 parts of glycidyl acrylate. This
mixture was spxead to a thickness of 3 mils on a glass plate
and irradiated for 20 seconds at a distance of 4 inches using
a G.E. H3T7 mercury lamp. The mixture was observed to have
polymerized, The polymer was soluble in methylene chloride
and was not crosslinked. This establishes that polymerization
was effected through the acrylate double bond.
Example 5.
A 1% solution of triphenylsulfonium chloride in a
1:1 mixture by weight of triallylisocyanurate and trimethylol-
propane trithioglycolate was applied onto an aluminum panel
as a 2 mil film. The 2 mil film was exposed to a G.E. H3T7
lamp for 15 seconds. A hard polymerized coating was obtained.
Example 6.
There was added to a mixture of 33% styrene and 67%
of the unsaturated polyester of Example 1, 1~ of S-phenylthi-
-14-
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RD-8618
oxanthilium hexafluoroarsenate of the formula
~ AsF6
~ , .
I'he above solul:ion was used to impregnate one layer of a glass
cloth. The impregnated cloth was then exposed to irradiation
from a G.E. H3T7 lamp at a distance of four inches for 1 minute.
After exposure, a rigid, cured composite was obtained.
In addition to the triarylsultonium salts of formulas
(1) and (23, triarylsulfonium salts which also can be used in
the practice of the invention to make photocurable compositions
are compounds oE the formula,
(3) [(R)a (Rl)b S]~rY']
where R is as previously defined, Rl is a divalent aromatic
or divalent heterocyclic, Y' can be Y when compounds of formula
~ (3) are used in place of compounds of formula (1) and Y' can
1~5 be X when compo~mds of formula (3) are used in place of compounds
~- of formula (2),
"a" is 1 or 3,
"b" is 0 or 1,
S has a valence of 3 which can be
satisfied by R alone or a combin-
ation of R and Rl.
Although the above examples are directed to only a
few of the very many variables contained in both the practice
of the method and the photocurable compositions of the present
invention, it should be understood that a much broader variety
of organic resins and triarylsulfonium salts can be used as
shown in the description preceding these examples.
-15-
