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Figure 8
20
18
16
1
14 Figure 11: PI-Spectral Response H Arc Lamp
Track-free Time (sec) 10 8 0.40
12
0.50

4 6 0.30
2 Absorbance
0 0.20
0 0.2 0.4 0.6 0.8 1 1.2
Dosage of DBA (PHR) 0.10
0.00
Formulation: Tetraacrylate monomer, PI: Iodonium Salt (4.1 phr,
200 250 300 350 400 450
Film Thickness 18 μm, OD value > 1.5, Light source: UV LED 365
Wavelength (nm)
nm (30mW/cm2) covered with PET
DEA DBA DETX
Figure 9
Figure 12
2000

1500
Track-freeTime (sec) 1000

500

0
UVS = UV Sensitizer 0 0.5 1
Dose of sensitizer (wt%)
DBA DETX
Formulation: Cycloaliphatic Epoxy, PI: Sulfonium salts 5 wt%,
Figure 10
Sensitizer: DBA or DETX diethyl thioxanthone, Blue pigments
160
(P.B.15): 30 wt%, thickness: 30 μm,
140
Light source: 365nm UV LED (< 1 mW/cm2)
120
100
Track-freeTime (sec) 80 without any sensitizer present. As the anthracene derivative DBA is
In this case, curing was negligible if the photoinitiator was used
60
40
20 added at increasing levels, the amount of time needed to achieve sur-
face cure drops dramatically.
0 Like the use of anthracene derivatives in free radical curing, these
0.2 0.4 0.6 0.8 1 2
sensitizers can also play a role in UV-LED cationic cure. The overall
Dosage of DBA (%)
mechanism is believed to be like the mechanism of anthracene deriva-
CPI-100P (Sulfonium salt) Omnicat 250 (Iodoinium salt)
tive sensitization in free radical cure mentioned earlier in this paper.
Formulation: Cycloaliphatic Epoxy, PI: Sulfonium or Iodonium, J. Myoung-Souk and J. Crivello have suggested the following process
Anthracene: DBA, Thickness: 5μm, Light source: UV LED 405nm for the role of anthracene derivatives in cationic cure (Figure 9)
(50mW/cm2)
The performance of the anthracene derivatives varies with the type
of photoinitiator used in cationic cure. Figure 10 illustrates the impact
After five minutes of exposure, the combination of the photoiniti- that the addition of DBA has on iodonium photoinitiators when com-
ator 907 and DBA outperformed both the use of 907 by itself and the pared to sulfonium initiators while cured using a 405 nm UV-LED
combination of 907 and ITX. In fact, the anthracene derivative lamp. DBA is particularly effective at a dose range of 0.4 – 0.6%.
DBA matched with the 907 photoinitiator gave essentially the same A traditional class of sensitizers used in cationic cure is thioxan-
conversion as TPO. To complete the work on free radical curing, we thones. When comparing the absorption spectra of DEA and DBA
examined the use of anthracene derivatives in pigmented coatings. with a typical thioxanthone DETX, one would predict that DEA, DBA
In this case, a simple black pigmented coating was cured using an and DETX would be interchangeable when it comes to their use in
iodonium salt as the photoinitiator. The Optical Density of the UV-LED cationic cure applications (Figure 11).
cured coating was greater than 1.5 and a UV-LED lamp at 365 nm In this case, the formulation tested contained 30 wt% blue
was used as the UV source (Figure 8). pigment. The use of pigments in cationic cure coatings and inks is
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