How to Choose a Photoinitiator for UV Curing: 1173, 184, 369, 907, TPO and Blends
September 3, 2026 · Technical
Start with the Application, Not the Trade Name
Photoinitiator selection in UV curing is a four-variable problem: absorption wavelength (does your lamp or LED emit there?), loading (cost vs cure depth), film properties (yellowing, migration, odor) and handling (liquid vs solid, melting point). Choosing a photoinitiator by trade name alone usually ends in a reformulation.
Type I Photoinitiators: The Standard Set
| Product | CAS | Absorption | Typical Use |
|---|---|---|---|
| 1173 | 7473-98-5 | 244/278/322 nm | Liquid, general-purpose; wood and basic coatings at 3–5% |
| 184 | 947-19-3 | ~245/280/333 nm | Low-yellowing clear coats, laminates, electronics |
| 907 | 71868-10-5 | 230–310 nm | Pigmented inks and thick layers; high activity |
| 369 | 119313-12-1 | ~232–366 nm | High-efficiency for pigmented systems |
| TPO | 75980-60-8 | 273/370 nm | Deep cure, LED-cure; photo-bleaching; 1–3% coatings, 5–10% inks |
| TPO-L | 84434-11-7 | ~273/380 nm | Liquid TPO alternative; easy dosing; LED systems |
Type II Systems and Blends
ITX and DETX are Type II initiators that absorb in the 350–400 nm range; they require amine co-initiators and are normally used in blends — for example with 184 or BP — to broaden absorption in pigmented inks and printed electronics.
Practical Rules of Thumb
- LED curing? Go TPO/TPO-L, optionally blended with 184 for balance. Standard 365/385/395 nm LEDs miss 1173 and 907 absorption peaks.
- Clear coat, low yellowing? 184 or blends with TPO; avoid high ITX loadings.
- White or pigmented ink? 369 and 907 are the high-activity standard; expect higher cost per kg but lower loading.
- Thick / 3D layers? Combine 184+TPO for surface and deep cure; photo-bleaching of TPO keeps the film clear.
- Food-contact packaging? Consider MBF and check migration limits with your converter.
Verify Before You Scale
Request a small sample (100 g–1 kg) and cure-test it under your real lamp. Check the batch COA for purity (≥98% HPLC/GC typical for these grades) and confirm the storage and handling requirements — our storage guide covers temperature, light and humidity risks that quietly reduce photoinitiator efficiency.