Abstract:
Iodonium and sulfonium photoinitiators are naturally sensitive to only a small portion of the electromagnetic spectrum. 
     Various classes of sensitizing dyes for iodonium and sulfonium salts are disclosed herein.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to iodonium and sulfonium compounds and, more particularly, to photosensitization of aromatic iodonium and sulfonium photoinitiators. 
     Iodonium and sulfonium salts are known to absorb ultraviolet light only at wavelengths below about 300 nm, and their absorption spectra are essentially independent of the anion portion of the molecule. This limited spectral response is accordingly a serious inherent limitation with respect to their use as photoinitiators in photosensitive compositions. For example, in the field of graphic arts, such as in the preparation of printing plates, a photographic film negative is disposed between the lamp and the photosensitive plate. This film negative prevents the transmission of appreciable light of wavelengths below about 340 nm. Furthermore, when photosensitive compositions are used as photocurable coatings, light of wavelengths below about 300 nm decreases in intensity as it passes through the coating, due to absorption of the light by the monomeric compounds, pigments, binders, etc., present in the coating. Either occurrence would reduce the usefulness of sulfonium and iodonium photoinitiators because of their limited spectral response. 
     Although there are dozens of known classes of dyes and other materials which can be used to broaden the spectral response of photosensitive compositions, it has not been possible to predict which materials would be useful in sensitizing aromatic iodonium and sulfonium salts. In fact, it has been found that only select materials are useful in sensitizing these aromatic salts. For example, a well known and widely used class of energy transfer sensitizers, known as triplet sensitizers, e.g., benzophenone, acetophenone, etc., are not significantly effective for sensitizing aromatic sulfonium and iodonium salts. U.S. Pat. No. 4,069,054 discloses certain amines and heterocyclic compounds which are useful sensitizers for sulfonium photoinitiators. U.S. Pat. No. 4,026,705 also discloses sensitizers for iodonium photoinitiators. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention there is provided a photosensitive admixture comprising an aromatic iodonium or sulfonium compound and a sensitizing compound selected from the class of polyarylenes, polyarylpolyenes, 2,5-diphenylisobenzofurans, 2,5-diarylcyclopentadienes, diarylfurans, diarylthiofurans, diarylpyrrols, polyarylphenylenes, coumarins, and polyaryl-2-pyrazolines. 
     There are many advantages associated with sensitized aromatic sulfonium compounds. For example, in photosensitive compositions the speed of light curing is increased, and safer and less expensive exposure lamps may be used effectively. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Aromatic sulfonium compounds which can be sensitized in accordance with this invention include those having the formulae: ##STR1## wherein R 1 , R 2 , and R 3  can be the same or different provided that at least one of such groups is aromatic. Such groups can be selected from aromatic groups having 4 to 20 carbon atoms (e.g., substituted or unsubstituted phenyl, naphthyl, thienyl, and furanyl. Substitution may be with such groups as alkoxy, alkylthio, arylthio, halogens, etc., and alkyl radicals having 1 to 20 carbon atoms. The term &#34;alkyl&#34; as used here is meant to include substituted alkyl radicals (for example, with substituents such as halogen, hydroxy, alkoxy, aryl). Preferably, R 1 , R 2  and R 3  are each aromatic. Z is selected from the group consisting of oxygen; sulfur; ##STR2## where R is aryl (of 6 to 20 carbons, such as phenyl) or acyl (of 2 to 20 carbons, such as acetyl, benzoyl, etc.); a carbon-to-carbon bond; or ##STR3## where R 4  and R 5  are selected from the group consisting of hydrogen, an alkyl radical having 1 to 4 carbon atoms, and an alkenyl radical having 2 to 4 carbon atoms; and n is zero or 1; and X -  is any anion. 
     Although, the particular nature of the anion, X, is not limiting or critical for the purposes of this invention (i.e., for the purposes of sensitizing the sulfonium cation), for many application it is preferred for the aromatic sulfonium compound to be in the form of a complex salt where X is selected from tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, hexafluoroantimonate, and hydroxypentafluoroantimonate (e.g., for photoinitiation of cationically polymerizable materials such as epoxy resins or epoxy resins and polyols). 
     Aromatic sulfonium salts are known and recognized in the art. Triaryl-substituted sulfonium compounds, for example, can be prepared by the procedures described in C. H. Wiegand et al., &#34;Synthesis and Reactions of Triarylsulfonium Halides&#34;, J. Org. Chem. 33, 2671-75 (1968). Aromatic sulfonium salts also having alkyl-substitution can be prepared by the procedures described in K. Ohkubo et al., J. Org. Chem. 36, 3149-55 (1971). The preferred method for making triaryl-substituted sulfonium compounds is described in U.S. Pat. No. 2,807,648, incorporated herein by reference, from which complex sulfonium salts can be made. The complex sulfonium salts can be prepared from the corresponding simple salts, such as the bisulfate or halide salts, by metathesis with a metal or ammonium salt or acid of the complex anion desired. 
     The sulfonium complex salts are substituted with at least one, and preferably three, aromatic groups. Representative groups are aromatic groups having 4 to 20 carbon atoms and are selected from phenyl, thienyl and furanyl groups. These aromatic groups may optionally have one or more fused benzo rings (e.g., naphthyl and the like; benzothienyl, dibenzothienyl; benzofuranyl, dibenzofuranyl; etc.). Such aromatic groups may also be substituted, if desired, by one or more of the following groups, or by other groups which are essentially non-reactive with other components present in the particular composition in which the complex salt is to be used: halogen, nitro, aryl, ester groups (e.g., alkoxycarbonyl such as methoxycarbonyl and ethoxycarbonyl, phenoxycarbonyl and acyloxy such as acetoxy and propionyloxy), alkoxy groups (e.g., methoxy, ethoxy, butoxy, and the like), aryl groups (e.g., phenyl), alkyl groups (e.g., methyl, ethyl, t-butyl and the like) aryloxy groups (e.g., phenoxy), alkyl-sulfonyl (e.g., methylsulfonyl, ethylsulfonyl, and the like) arylsulfonyl groups (e.g., phenylsulfonyl groups), hydrocarbylthio groups (e.g., p-phenylthio, methylthio, etc.), perfluoroalkyl groups (e.g., trifluoromethyl, perfluoroehtyl, and the like), and perfluoroalkylsulfonyl groups (e.g., trifluoromethylsulfonyl, perfluorobutylsulfonyl, and the like). 
     Examples of suitable aromatic sulfonium complex salt photoinitiators include: 
     triphenylsulfonium tetrafluoroborate 
     methyldiphenylsulfonium tetrafluoroborate 
     dimethylphenylsulfonium hexafluorophosphate 
     triphenylsulfonium hexafluorophosphate 
     triphenylsulfonium hexafluoroantimonate 
     diphenylnaphthylsulfonium hexafluoroarsenate 
     tritolysulfonium hexafluorophosphate 
     anisyldiphenylsulfonium hexafluoroantimonate 
     4-butoxyphenyldiphenylsulfonium tetrafluoroborate 
     4-chlorophenyldiphenylsulfonium hexafluorophosphate 
     tri(4-phenoxyphenyl)sulfonium hexafluorophosphate 
     di(4-ethoxyphenyl)methylsulfonium hexafluoroarsenate 
     4-acetonylphenyldiphenylsulfonium tetrafluoroborate 
     4-thiomethoxyphenyldiphenylsulfonium hexafluorophosphate 
     di(methoxysulfonylphenyl)methylsulfonium hexafluoroantimonate 
     di(nitrophenyl)phenylsulfonium hexafluoroantimonate 
     di(carbomethoxyphenyl)methylsulfonium hexafluorophosphate 
     4-acetamidophenyldiphenylsulfonium tetrafluoroborate 
     dimethylnaphthylsulfonium hexafluorophosphate 
     trifluoromethyldiphenylsulfonium tetrafluoroborate 
     p-(phenylthiophenyl)diphenylsulfonium hexafluoroantimonate 
     10-methylphenoxathiinium hexafluorophosphate 
     5-methylthianthrenium hexafluorophosphate 
     10-phenyl-9,9-dimethylthioxanthenium hexafluorophosphate 
     10-phenyl-9-oxothioxanthenium tetrafluoroborate 
     5-methyl-10-oxothianthrenium tetrafluoroborate 
     5-methyl-10,10-dioxothianthrenium hexafluorophosphate 
     Of the aromatic sulfonium complex salts which are used in this invention the preferred salts are the triaryl-substituted salts such as triphenylsulfonium hexafluorophosphate, p-(phenylthio)phenyldiphenylsulfonium hexafluoroantimonate and triphenylsulfonium hexafluoroantimonate. The triaryl-substituted salts are preferred because they are more thermally stable than the mono- and diaryl substituted salts and accordingly may be used in one-part curable systems where long shelf life is desired. The triaryl-substituted complex salts are also more amenable to dye sensitization in accordance with this invention. 
     Aromatic iodonium salts which can be sensitized in accordance with this invention include those having the formulae: ##STR4## wherein Ar 1  and Ar 2  are aromatic groups having 4 to 20 carbon atoms and are preferably selected from phenyl, naphthyl, thienyl, furanyl and pyrazolyl groups; 
     W is selected from ##STR5##  where R 6  is aryl of 6 to 20 carbon atoms or acyl of 2 to 20 carbon atoms (such as substituted or unsubstituted phenyl, acyl, benzoyl, etc. as described above for two sulfonium photoinitiators); a carbon-to-carbon bond; or ##STR6##  where R 7  and R 8  are selected from hydrogen, alkyl groups of 1 to 4 carbon atoms, and alkenyl groups of 2 to 4 carbon atoms; and b is zero or 1; and Q is any anion (as described above for X - ) and preferably a halogen-containing complex anion selected from tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, hexafluoroantimonate. 
     Amongst the useful iodonium salts are particularly included 
     diphenyliodonium iodide 
     diphenyliodonium hexafluoroantimonate 
     4-chlorophenylphenyliodonium tetrafluoroborate 
     di(4-chlorophenyl)iodonium hexafluoroantimonate 
     diphenyliodonium hexafluorophosphate 
     diphenyliodonium trifluoroacetate 
     4-trifluoromethylphenylphenyliodonium tetrafluoroborate 
     diphenyliodonium hexafluoroarsenate 
     ditolyliodonium hexafluorophosphate 
     di(4-methoxyphenyl)iodonium hexafluoroantimonate 
     di(4-methoxyphenyl)iodonium chloride 
     (4-methylphenyl)phenyliodonium tetrafluoroborate 
     di-(2,4-dimethylphenyl)iodonium hexafluoroantimonate 
     di-(4-t-butylphenyl)iodonium hexafluoroantimonate 
     2,2&#39;-diphenyliodonium hexafluorophosphate. 
     The amount of latent photocatalytic onium salt used in the photopolymerizable compositions of the invention is not critical but can be from about 0.01 to about 10.0% by weight of polymerizable material and preferably 0.1 to 5% by weight of the total weight of polymerizable material. The use of greater amounts of onium salt generally does not afford increased polymerization and the use of less tends to reduce the extent of polymerization. The compositions of the invention are prepared by mixing the onium salt with the polymerizable material until a solution is formed. Because some of the onium salts may have limited solubility in the polymerizable composition, it is preferable to first dissolve the onium salt in a liquid diluent that is inert to the components of the composition and then mix this solution into the polymerizable mixture. Suitable inert diluents include alcohols such as ethanol, ketones such as acetone, halohydrocarbons such as dichloromethane. 
     The compositions of the invention can be used for preparation of coatings for various substrates; however, adhesives, sealants, binders and rubbers can also be prepared from the compositions of the invention and are particularly useful where such materials need be polymerized in situ by irradiation. The compositions of the invention can be applied to substrates by spraying, brushing, dipping, roller coating, flow coating or any of the methods used in commercial coating operations. 
     The compositions of the invention may contain certain additives to alter the properties of the polymerized or cured product. Thus, there may be added dyes, pigments, plasticizers, fillers and the like as long as these materials do not prevent sufficient penetration into the composition by radiation absorbed by the sensitizer. 
     The polymerization or curing of the composition is a triggered reaction, i.e., once degradation of the photocatalytic onium salt has been initiated, the polymerization or curing proceeds and will continue even after terminating radiation. The use of thermal energy during or after exposure to radiation greatly accelerates polymerization or curing. 
     Generally speaking, the sensitized aromatic iodonium and sulfonium complex salts are significantly useful as photoinitiators for cationic reactions (such as polymerization of cationically polymerizable monomers). For example, the sensitized complex salts with appropriate anions are particularly suitable as photoinitiators for the polymerization or copolymerization of cationically polymerizable monomers such as epoxides (epoxy resins), epoxides and polyols, oxetanes, vinyl ethers, lactones, etc. The sensitized complex salts are also useful as photoinitiators for free-radical polymerization (e.g., polymerization of vinyl or acrylic monomers and others such as acrylate esters, acrylamide esters, acrylonitrile, styrene, butadiene, vinylidenes, etc.) and polymerization by hydrolysis of silanes (as in U.S. Pat. No. 4,101,513). 
     Generally speaking, the amount of sensitizer used in the practice of this invention is about 0.01 to 10 parts, and preferably about 0.1 to 1 part, by weight of sensitizer per part of aromatic complex salt. Factors to consider in determining the amount of sensitizer to be included in a given composition include intended light exposure conditions, thickness of the composition to be cured, solubility of the sensitizer in the composition, and other factors normally considered in the utilization of sensitizers. Of course, more than one photoinitiator and/or sensitizer may be used in a single composition. 
     The sensitizing compounds of the present invention are fluorescent polyaryl compounds selected from the group consisting of polyarylenes, polyarylpolyenes, 2,5-diphenylisobenzofurans, 2,5-diarylfurans, 2,5-diarylthiofurans, 2,5-diarylpyrroles, 2,5-diarylcyclopentadienes, polyarylphenylenes, coumarins, and polyaryl-2-pyrazolines. These compounds may be partially described by the following general formulae: 
     
         R.sup.9 --Q--R.sup.10                                      I 
    
     wherein 
     R 9  and R 10  are independently selected from aryl groups comprising phenyl, napthyl, biphenyl, 2-furanyl groups (all of which may be substituted or not), and 
     Q is ##STR7##  wherein R 11 , R 12  and R 13  are independently H or a phenyl group (i.e., substituted or not), and is preferably H, 
     R 14  is selected from --CH═CH--, ##STR8##  wherein R 15  and R 16  are H, methyl, methoxy, or phenyl when X is O, and H or phenyl when X=S, ##STR9## R 17  and R 18  are H or a styryl group (i.e., substituted or not), or a stilbenyl groups (i.e., substituted or not); 
     X is O, S, ##STR10##  where R 19  is H or phenyl; a and c are independently 0 or 1; and b is 0, 1, 2, 3, or 4 and the sum of a+b+c is 1 to 4; 
     
         R.sup.20 --R.sup.21                                        IV 
    
      wherein 
     R 20  is a 2-pyrazoline of the structure ##STR11##  wherein R 22  is a phenyl, biphenyl group (preferable substituents being selected from lower alkyl, lower alkoxy, halogen, lower alkylamino, alkylsulfonyl, p-acetamido, sulfonamido, and carbalkoxy); 
     R 23  and R 24  are independently H, lower alkyl, phenyl, biphenyl, or naphthyl groups (the preferred substituents on the phenyl and naphthyl group being lower alkyl, lower alkoxy, lower alkylamino, carbalkoxy, sulfonamido and acetamido; and 
     R 21  is R 20  or phenyl, biphenyl, naphthyl, or a styryl group (substituted or not, with preferred substituents being lower alkyl, lower alkoxy, lower alkylamino, halogen and acetamido; ##STR12##  wherein R 25  is lower alkyl or perfluoro (lower) alkyl, 
     R 26  is 2-benzothiazolyl, carboalkoxy, lower acyl (1 to 5 carbon atoms), aryl (preferably phenyl), or cyano, and R 25  and R 26  together form a 5-membered ring, 
     R 27  is lower alkylamino, 
     R 28  and R 29  are H or together with R 27  form a quinolizino ring fused to the phenyl ring; and ##STR13##  wherein R 30  and R 31  are independently H or phenyl groups, (substituted or not, e.g., with lower alkoxy), 
     R 32  and R 33  are independently H, phenyl, (substituted or not, e.g., with lower alkoxy), lower alkyl, or lower alkoxy, and 
     R 34  and R 35  are independently H, lower alkyl, and phenyl. 
     Where the term &#34;lower&#34; is used in desribing an organic group it means that there are no more than 5 carbon atoms present in the lower group. 
     There are a number of different classes of compounds which may be used as photosensitizers according to the practice of the present invention. These classes include, for example, the polyarylenes, the 1,3-diaryl-2-pyrazolines, the substituted coumarins, and the isobenzofurans. Examples of these compounds appear below according to their respective classes. The examples refer to these compounds by their numbers. 
     A. Polyarylenes 
     1. p,p&#39;-dimethoxystilbene 
     2. 1,4-diphenyl-1,3-butadiene 
     3. 1-phenyl-4-(chlorophenyl)-1,3-butadiene 
     4. 1,4-bis-(p-methoxyphenyl)-1,3-butadiene 
     5. 1,4-bis-(p-tolyl)-1,3-butadiene 
     6. 1,1,4,4-tetraphenyl-1,3-butadiene 
     7. 1,6-diphenyl-1,3,5-hexatriene 
     8. 1-(2-naphthyl)-4-phenyl-1,3-butadiene 
     9. 1-(2-furyl)-4-phenyl-1,3-butadiene 
     10. 1,4-di-(2-naphthyl)-1,3-butadiene 
     11. 1-(p-biphenyl)-1,3-butadiene 
     12. 1,8-diphenyl-1,3,5,7-octatetraene 
     13. 1,4-di-(2-methylstyryl)benzene 
     14. 1,3,5-tristyrylbenzene 
     15. 2,6-distyrylnaphthalene 
     16. 4-styryl-p-biphenyl 
     17. 1,3,5-tris-(p-methoxystyryl)-benzene 
     18. 1,3,4-tri-(p-methoxystyryl)-benzene 
     19. 1,2-di-(3,4-dimethoxystyryl)-benzene 
     20. 1,3,5-tri-(p-methoxystilbenyl)-benzene 
     21. 1,1-diphenyl-2-(p-methoxystilbenyl)-ethylene 
     22. 1,3-di-(p-methoxystyryl)-naphthalene 
     23. 2,5-diphenylfuran 
     24. 2,5-distyrylfuran 
     25. 2,3,4,5-tetraphenylfuran 
     26. 2,5-diphenyl-3-methoxyfuran 
     27. 2,5-diphenyl-4-methylfuran 
     28. 2,5-diphenylthiophene 
     29. 2,5-distyrylthiophene 
     30. 2,5-diphenylpyrrole 
     31. 1,2,5-triphenylpyrrole 
     32. 2,3,4,5-tetraphenylpyrrole 
     33. 1,2,3,4-tetraphenylcyclopentadiene 
     The above compounds can be prepared by referring to the following procedures: 
     Y. Hirshberg et al J.A.C.5., 72, 5120 (1950) 
     A. Siegrist et al U.S. Pat. No., 3,991,049 (260/240D) 
     E. Seus, J. Het. Chem., 2, 318 (1965) 
     S. King et al, J. A. C. 5, 73, 2253 (1951) 
     B. 1,3-diaryl-1-pyrazolines 
     34. 1,3-diphenyl-2-pyrazoline 
     35. 1-p-methoxyphenyl-3-phenyl-2-pyrazoline 
     36. 1-phenyl-3-p-cyanophenyl-2-pyrazoline 
     37. 1-phenyl-3-styryl-2-pyrazoline 
     38. 1-naphthyl-3-phenyl-2-pyrazoline 
     39. 1-p-chlorophenyl-3-phenyl-2-pyrazoline 
     40. 1-m-chlorophenyl-3-(2,4-dimethoxyphenyl)-2-pyrazoline 
     41. 1-(3,4-dichlorophenyl)-3-phenyl-2-pyrazoline 
     42. 1-p-methylsulfonylphenyl)-3-phenyl-2-pyrazoline 
     43. 1-p-acetamidophenyl-3-phenyl-2-pyrazoline 
     44. 5-isopropyl-1,3-diphenyl-2-pyrazoline 
     45. 1-p-tolyl-3-phenyl-2-pyrazoline 
     46. 1-p-carbomethoxyphenyl-3-phenyl-2-pyrazoline 
     47. 1,3-diphenyl-5-p-acetamidophenyl-2-pyrazoline 
     48. 1,3,4,5-tetraphenyl-2-pyrazoline 
     49. 1,5-diphenyl-3-styryl-2-pyrazoline 
     50. 1-phenyl-3-(p-methoxystyryl)5-(p-methoxyphenyl)-2-pyrazoline 
     51. 1-phenyl-3-(-diethylaminostyryl)-5-(diethylaminophenyl)-2-pyrazoline 
     52. 1-(p-methoxyphenyl)-3-(p-diethylaminostyryl)-5-(diethylaminophenyl)-2-pyrazoline 
     53. 1,1&#39;-diphenyl3-3&#39;-bis-2-pyrazoline 
     54. 1-p-biphenyl-3,5-diphenyl-2-pyrazoline 
     55. 1-phenyl-3-(2-naphthyl-5-(p-biphenyl)-2-pyrazoline 
     56. 1,3-diphenyl-5-(9-anthryl)-2-pyrazoline 
     57. 1-phenyl-3-(p-biphenyl-5-(p-isopropylphenyl)-2-pyrazoline 
     58. 1,3-diphenyl-5-naphthyl-2-pyrazoline 
     These compounds can be preared by referring to the following publications: 
     A. Wagner et al, Angew. Chem. Int. Ed., 5,699 (1966) 
     R. H. Wiley et al, J. Org. Chem., 23, 732 (1958) 
     N. A. Evans et al, Aust. J. Chem., 27, 2267 (1974) 
     R. Maruyama et al, Chem. Abst. 65, 13850 (1966) 
     Neth. Appl. 6,506,722, Chem. Abst., 64, 19851c (1966) 
     C. Isobenzofurans 
     59. 1,3-diphenylisobenzofuran 
     60. 1,3-diphenyl-4,7-di-(p-methoxyphenyl)isobenzofuran 
     61. 1,3-di-(p-methoxyphenyl)-3,6-diphenylisobenzofuran 
     62. 1,3,4,7-tetra-(p-methoxyphenyl)isobenzofuran 
     63. 1,3,4,7-tetraphenylisobenzofuran 
     64. 1,3-di-(p-methoxyphenyl)isobenzofuran 
     65. 1,3-di-(p-biphenyl)isobenzofuran 
     66. 1,3-diphenyl-5,6-dimethylisobenzofuran 
     67. 1,2-diphenyl-5-methylisobenzofuran 
     68. 1,3,5,6-tetraphenylisobenzofuran 
     69. 1,3-di-(p-biphenyl)-4,7-diphenylisobenzofuran 
     70. 1,3,4,7-tetra-(p-methoxyphenyl)isobenzofuran 
     These compounds are prepared by methods described in: 
     A. Zweig et al, J. Am. Chem. Soc., 89, 4091 (1967) 
     R. Adams and M. H. Gold., J. Am. Chem. Soc., 62, 2038 (1940) 
     D. Substituted Coumarins 
     71. 7-diethylamino-4-methylcoumarin 
     72. 7-dimethylamino-4-trifluoromethylcoumarin 
     73. 7-diethylamino-3,4-cyclopentylcoumarin 
     74. 7-dimethylamino-3-phenylcoumarin 
     75. 3-(2&#39;-benzothiazolyl)-7-diethylaminocoumarin 
     76. 7-methoxy-4-methylcoumarin 
     77. 1,2,4,5,3H,6H,10H-tetrahydro-9-carbethoxy-[1]-benzopyrano-(9,9a,1-gh)quinolizin-10-one 
     78. 1,2,4,5,3H,6H,10H-tetrahydro-9-cyano-[1]-benzopyrano-(9,9a,1gh)quinolizin-10-one 
     79. 1,2,4,5,3H,6H,10H-tetrahydro-9-acetyl-[1]-benzopyrano-(9,9a-1-gh)quinolizin-10-one 
     The above compounds are commercially available. 
    
    
     The invention is further illustrated by means of the following examples wherein the term &#34;parts&#34; refers to parts by weight unless otherwise indicated. 
     EXAMPLES 1-9 
     A stock solution was prepared from 50 parts of a 5% by weight solution of polyvinylbutyral in tetrahydrofuran, 0.5 parts of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, and 0.2 parts of diphenyl iodonium hexafluorophosphate. To 5 parts of this solution was added 5×10 -5  moles of sensitizer described in the present invention. These solutions were then knife coated (5×10 -2  mm wet) onto a polyester film base then oven dried at 60° C. for 5 minutes. The dried film samples were then exposed to a 500 watt ultraviolet lamp at a distance of 17.8 cm through a photographic step wedge in contact with the film side of the sample. After exposure, each sample was well sprayed with methanol to wash away the soluble unpolymerized material. Table I (under Exposure Time) shows the number of solid, insoluble steps remaining after the spraying. This provides a relative measure of the cure rate and sensitivity of the solutions. 
     
                       TABLE I______________________________________          Exposure Time (min.)Example   Sensitizer 0.25     0.50   1.0______________________________________1         none       0        0      02         1          0        2      43         2          0        1      64         4          0        1      35         6          1        5      86         7          6        8      &gt;107         8          2        6      &gt;108         12         0        0      39         13         1        3      6______________________________________ 
    
     EXAMPLES 10-15 
     A stock solution was prepared from 20 parts of an epoxy cresol novolac resin (having a melting point of 85°-90° C. and an epoxide equivalent weight of 235), 30 parts acetone, and 0.4 parts of triphenylsulfonium hexafluorophosphate. To 5 parts of this solution was added 0.013 parts of various sensitizers according to the present invention. The solutions were then coated, dried, and exposed as in Examples 1-9. Table II shows the number of solid steps remaining after washing thoroughly with acetone. 
     
                       TABLE II______________________________________             Exposure Time (min).Example    Sensitizer   5         10______________________________________10         none         0         011          7           712          8           813         34           714         28           315         59           7______________________________________ 
    
     EXAMPLES 16-21 
     The stock solution of Examples 1-9 with 0.2 g of diphenyliodonium hexafluoroarsenate in place of the earlier photoinitiator was used in the following examples. To 5 parts of this solution were added 0.01 parts of a sensitizer of this invention. These solutions were coated, dried, exposed and washed as in Examples 1-9. Table III shows the number of solid steps remaining after washing with methanol. 
     
                       TABLE III______________________________________         Exposure Time (min).Example  Sensitizer 1.5     2.0    3.0   10______________________________________16       none       0       0      0     017       71         0       0      418       72         8       &gt;1019       75         0       0      220       77         6       821       79         7       9______________________________________ 
    
     EXAMPLES 22-35 
     A stock solution was prepared from 100 parts of a 5% by weight solution of polyvinyl butyral in tetrahydrofuran, 1.0 parts of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, and 0.4 parts of diphenyliodium tetrafluoroborate (DPIT), tri(p-methoxyphenyl)sulfonium hexafluorophosphate (TMSH), or diphenylmethylsulfonium hexafluorophosphate (DPSH). To 5 gram portions of these solutions were added 10 mg of a sensitizer of the present invention. These solutions were coated, dried, exposed and washed as in Examples 1-9. The results are shown in Table IV. 
     
                       TABLE IV______________________________________            Exposure Time (min).   OniumExample Salt     Sensitizer                      1    2     4______________________________________22      DPIT     none      0    0     0 (10 min)23      DPIT      6        624      DPIT     28        425      DPIT     34        1026      TMSH     none      0    0     0 (10 min)27      TMSH     16                   228      TMSH     21                   229      TMSH     34                   730      TMSH     68                   331      DPSH     none      0    0     0 (10 min)32      DPSH      7             333      DPSH     13             134      DPSH     42             735      DPSH     59             3______________________________________ 
    
     EXAMPLES 36-40 
     To 5 parts of a diglycidyl ether of bisphenol A epoxy resin having an epoxide equivalent weight of 178 was added 2% by weight of a 50/50 mixture of triphenylsulfonium hexafluoroantimonate and (p-phenylthiophenyl)-diphenylsulfonium hexafluoroantimonate. This solution was then coated as in Examples 1-9. Examples of the coatings were then exposed through a Corning Glass Filter No. 0-52 (which transmits only light having a wavelength greater than 334 nm) with a 275 watt sunlamp at a distance of 12.7 cm. The exposure times required to provide a tack free surface (S) and a tack free lower portion (L) were recorded and are shown in Table V. 
     
                       TABLE V______________________________________            Exposure Time (min)Examples  Sensitizer   (S)        (L)______________________________________36        none         10         1037        53           2          538        49           0.5        139        50           0.67       1.3340         8           5          9______________________________________ 
    
     EXAMPLES 41-45 
     Examples 36-40 were repeated except that the epoxy resin was replaced by 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate and the photoinitiator was replaced by a 50/50 mixture of triphenylsulfonium hydroxypentafluoroantimonate and (p-phenylthiophenyl)diphenylsulfonium hydroxypentafluoroantimonate. The results are shown in Table VI. 
     
                       TABLE VI______________________________________            Exposure Time (min)Example   Sensitizer   (S)        (L)______________________________________41        none         &gt;10        &gt;1042        49           1.5        343        50           1.5        344        72           4          545        79           2          4______________________________________ 
    
     EXAMPLES 46-52 
     A stock solution was prepared from 40 parts of 3,4-epoxycyclohexyl-3,4-epoxycyclohexane carboxylate and 0.8 parts of di-(p-tolyl)iodonium hexafluoroantimonate. 10 mg of the indicated sensitizing dyes were dissolved in 5 g portions of the stock solution and knife coated at 5.08×10 -2  mm wet on polyester film. The samples were exposed through the previously described glass filter No. 0-52 that transmits only light having a wavelength greater than 334 nm. Exposure was to the same lamp and the same distance as Examples 36-40. The results are shown in Table VII. 
     
                       TABLE VII______________________________________            Exposure Time (sec)Example Sensitizing Dye                  (S)        (L)______________________________________46      41             45         7547      42             20         4048      34             25         5049      17             30         6550*     63             300        36051*     59             20         4052      none           &gt;600       &gt;600______________________________________ *also contains 10 mg 2,6di-t-butyl-4-methylphenol- 
    
     EXAMPLES 53-55 
     A stock solution of 1.3 parts of pentaerythritol triacrylate, 1.16 parts of polymethylmethacrylate, 0.13 parts of phenyl(p-methoxyphenyl)-iodonium trifluoroacetate, and 14.8 parts of acetone was prepared. 10 mg of each of the sensitizers in Table VIII were dissolved in each of 5 g samples of the stock solution and coated and evaluated as described in Examples 1-9 except exposures were made in a Colight exposure apparatus containing a 400 watt mercury lamp. Acetone was used to dissolve away the unpolymerized material. The table shows the number of steps remaining after washing. 
     
                       TABLE VIII______________________________________            Exposure Time (min)Example   Sensitizer   1.0         5.0______________________________________53        none          0          054        34           10 (steps)55         7            3 (steps)______________________________________ 
    
     EXAMPLES 56-68 
     The Example 53-55 were exactly repeated replacing the iodonium initiator with triphenylsulfonium hexafluorophosphate. The Table IX shows the results as described above. 
     
                       TABLE IX______________________________________             Exposure Time (min)Example    Sensitizer   2.0        5.0______________________________________56         none         0          057         34           558          7           2______________________________________