Oxygen Inhibition and Photon Competition in Thin Pigmented Radiation-Curable Films: Why Surface Cure Governs Graphic Ink Performance

A thin pigmented UV-curable ink can fail at the air interface even when the layer beneath has polymerised substantially. Oxygen continuously competes for radical species at the free surface, while pigment and photoinitiator compete for the incident photons that create those radicals. The practical consequence is that nominal lamp dose, bulk conversion, hardness or apparent dryness cannot be used interchangeably. Graphic-ink qualification must explicitly resolve the surface state, the through-film state and the spectral-optical state that couples them.