CA1120180A - Free radical and cationically curable composition containing a triarylsulfonium salt photoinitiator - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Photocurable compositions are provided based on the use of particular triarysulfonium salts as photoinitiators for certain oxirane containing aliphatically unsaturated organic resins, such as acrylics, or mixtures of vinyl aromatic and unsaturated polyesters. A simultaneous free-radical cure and cationic cure of the aforesaid organic resins are achieved, which provides improved results, such as metal coatings having improved solvent resistance.

Description

~ 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.

11~0180 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 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 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 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 l~Z0~80 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 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 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, 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.

Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition curable by a simultaneous free-radical and cationic cure, comprising:
(A) a mixture of an aliphatically unsaturated organic material free of oxirane oxygen and an oxirane-containing monomeric or polymeric organic material, and (B) 0.1% to 15% by weight of (A) of a triarylsulfonium salt as a photoinitiator and having the formula [(R)a (R1)b S]+ [MQd]-where R is a monovalent aromatic organic radical selected from the group consisting of C(6-13) aromatic hydrocarbon radicals, heterocyclic radicals and substituted derivatives thereof;
R1 is selected from the group consisting of divalent aromatic hydrocarbon radicals, divalent heterocyclic radicals and substituted derivatives thereof;
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, 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.

2. The composition of claim 1, wherein the triaryl-sulfonium salt is a triphenylsulfonium salt.

3. The composition of claim 1, wherein the triarylsulfonium salt is triphenylsulfonium hexafluoroarsenate.

4. The composition of claim 1, wherein the photo-curable composition is a mixture of an epoxy resin, an unsaturated polyester and styrene.

5. The composition of claim 1, wherein the photocurable composition is a mixture of an epoxy resin, methylmethacrylate and polymethylmethacrylate.

6. The composition of claim 1, wherein the aliphatically unsaturated organic material free of oxirane oxygen is a polyacrylate.

7. The composition of claim 1, wherein the aliphatically unsaturated organic material free of oxirane oxygen is trimethylolpropane triacrylate.