IPDI Isocyanurate Trimer Non-Yellowing Hardener

IPDI (isophorone diisocyanate) is a cycloaliphatic isocyanate—its NCO groups are attached to a saturated ring rather than an aromatic ring. When the cured film is exposed to UV, there are no aromatic amine groups produced (which would oxidize to yellowing chromophores like quinone-imines). IPDI trimer films retain >95% of initial whiteness after 1000 hours QUV-A weathering, while TDI-based systems typically yellow (ΔYI >10) within 200 hours. IPDI systems also maintain higher hardness retention at elevated temperatures. The trade-off is slower reactivity and higher cost, making IPDI trimer the standard choice for exterior-grade automotive clearcoats and architectural polyurethane topcoats where appearance retention is mandatory.