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PAINT & COATINGS MANUFACTURING: UV PHOTOINITIATORS

THE USE OF ANTHRACENE

DERIVATIVES IN UV-LED CURING

By Dr. Mike J. Idacavage

here is a strong interest in UV-LED curing of coatings, inks, Anthracene derivatives are a potential solution to broadening the
adhesives, etc., due to the benefits of using UV-LED as the range of photoinitiators that can be used with UV-LED lamps. Table
Tenergy source. To meet the end user’s needs, resin formula- 1 lists a few common anthracene derivatives that are commercially
tors need to draw on the list of available materials. While the range of available (trade names are UVS-1101 and UVS-1331).
monomers and oligomers that can be used is quite large, formulators
are somewhat limited by the photoinitiators available. The UV-LED Table 1
lamps that are most used today further limit the available useful
Chemical Name 9,10-DiButoxyAnthracene 9,10-DiEthoxyAnthracene
photoinitiator options. Currently, TPO is one of the more popular
photoinitiators. However, recent shortages in the availability Abbreviation DBA DEA
and impending regulatory reclassification of TPO have focused
attention on the limited options a formulator has when using a
Structure
UV-LED lamp for curing.
One of the key conditions that formulators must consider is how
well the photoinitiator absorption bands will overlap with the wave- Typical Appearance: Yellow powder Appearance: Yellow powder
lengths emitted by the light source. For Arc and microwave lamps, Characteristics Purity: 98% or more Purity: 97% or more
this is easy as both types of lamps produce UV energy in a wide
assortment of wavelengths resulting in a high probability that there 9,10-DiButoxyAnthracene (DBA) and 9,10-DiEthoxyAnthracene
will be overlap. Figure 1 shows a typical H Arc lamp emission with (DEA) both absorb at wavelengths that overlap well with the
several common photoinitiator absorptions. Both CPK (Cyclohexyl- currently available UV-LED lamps on the market. (Figure 3)
Phenyl Ketone) and TPO (Trimethylbenzoyl Phosphine Oxide) can Although both DBA and DEA absorb energy at wavelengths such
be used with an Arc lamp and H bulb combination. as 385 nm and 405 nm produced by commercially available UV-LED
UV-LED lamps are not so forgiving. A characteristic of an lamps, they cannot form free radical species by themselves.
UV-LED lamp is the production of very narrow UV wavelength However, they can transfer energy to photoinitiators that absorb at
emissions. This results in a high probability that the photoinitiator lower wavelengths which can then produce free radical species.
absorptions and the lamp emissions will not overlap as can be seen in These free radical species are then able to initiate polymerization.
Figure 2. While CPK is not sensitive to the UV-LED lamp in this The mechanism by which the anthracene derivatives transfer
case, there is enough absorption by TPO to allow it to react. This is a energy is not clear and is now under investigation in the lab. Based on
key reason why TPO is one of the preferred photoinitiators when data to date, the energy is transferred by either a Triplet Energy
using a UV-LED lamp. Another factor is the cost advantage that TPO Transfer process or an Excited State Energy Transfer (Table 2).
has over other photoinitiators such as BAPO that are effective when TPO is an excellent photoinitiator due to its ability to absorb at
using UV-LEDs as the light source. wavelengths that are emitted by 385- and 405-nm UV-LED lamps.

1 1
Figure 1: PI-Spectral Response H Arc Lamp Figure 2: PI – Spectral Response UV-LED
395
385

365

200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440 450 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440 450
H Lamp CPK TPO H Lamp CPK TPO
1 Miltec UV 1 Miltec UV

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