Cationic Photoinitiator CPI-6976 (Hexafluorophosphate Iodonium Salt)

Cationic UV cure (using epoxy resins + iodonium/sulfonium photoinitiators) offers several advantages over radical cure: (1) No oxygen inhibition—cationic polymerization proceeds in air without nitrogen inerting; (2) Low shrinkage—ring-opening of epoxides has <1% volumetric shrinkage vs. 5–15% for acrylate radical cure, critical for dimensional stability in electronics; (3) Post-cure continuation—cationic cure continues after UV exposure as long as acid and monomer are present; (4) Excellent adhesion to metals. The drawback is moisture sensitivity: humidity quenches the super-acid catalyst, so cationic cure requires low-humidity environments.