In recent years, the application of pigment in UV curing system is more and more popular. The addition of various colors not only enriches the products, but also brings some curing problems:

1. The film of pigmented coating can be in a wide range. Through curing for thick film is harder to achieve.
2. Pigments also absorb UV light. When the light absorption of pigments is stronger than that of UV photoinitiators, the curing effect is certainly not good.

To choose efficient UV photoinitiators for pigmented coating, we need to consider above two points.

Curing of thicker pigmented coatings advanced significantly in the mid-to-late 1990s with the introduction of the BAPO (bis acyl phosphine oxide) class of initiators. With the 1997 worldwide commercialization of Irgacure 819, it became possible to cure the entire range of pigmented coatings from white to black, and the entire color spectrum in between. The combination of Irgacure 819 with Irgacure 184 at ratios from 1:2 to 1:1 have proven most successful, delivering an excellent balance between surface and through curing without the need to use specially adapted lamp arrangements.

The light absorption spectrum of different pigments can tell us that the light absorption of the pigment is relatively weak in a certain wave spectrum, so the initiator with strong absorption capacity in this wave spectrum can achieve the fastest curing speed. So pick the UV photoinitiator with different light absorption spectrum to the pigment’s. And because the absorption spectrum of photoinitiator ITX is mostly not in the spectrum range of the existing pigments, the addition of photoinitiator ITX to the pigmented system will help to improve the curing speed.

General recommendation for some pigmented coatings:

Black coating – Irgacure 819;
Ultramarine coating – photoinitiator ITX , Irgacure 819;
Yellow coating – Irgacure 907 > Irgacure 369 > Irgacure 819;
Red coating – Irgacure 369 > Irgacure 907 > Irgacure 819;