UV-Curable Inks Chemicals

UV offset inks use highly viscous epoxy acrylate or polyester acrylate oligomers — offset requires high-tack, high-viscosity inks. UV flexo inks require lower viscosity and use reactive diluent-heavy formulations with polyester acrylate or urethane acrylate as binders. UV inkjet inks are the lowest viscosity (<30 mPa·s at jetting temperature) and rely heavily on reactive monomers.

For LED UV curing at 365/385/395 nm, acylphosphine oxide photoinitiators (BAPO, TPO-L, Irgacure 819) are most effective due to their broad absorption extending to 400+ nm. Phenyl glyoxalate derivatives and bis-acylphosphine oxides provide good through-cure in pigmented formulations. Conventional benzophenone has insufficient absorption at LED wavelengths.

For food contact packaging, photoinitiators must meet strict migration limits. EuPIA guidelines and Swiss Ordinance SR 817.023.21 specify permitted photoinitiators and migration limits. Polymeric photoinitiators and high-MW oligomeric initiators are preferred for food contact UV inks as they have negligible migration due to molecular size.

Reactive monomers (TPGDA, HDDA, NVC, GPTA) reduce viscosity and become part of the cured film through copolymerization with oligomers. Trifunctional monomers raise crosslink density and hardness; NVC improves adhesion to plastics; mono-functional monomers (NVP, IBOA) add flexibility but slow cure. Toxicology profile and migration potential dictate which monomers are food-contact compliant under EuPIA and Swiss Ordinance.

UV offset inks must maintain printability — low misting, good water/ink balance — at the high-tack viscosity offset requires. Higher pigment loading (15–18% cyan, 12–14% yellow) gives stronger color but stiffer ink. Synergists (waxes, oligomeric flow agents) reduce misting. Custom dispersants developed for UV systems prevent pigment migration and ensure stable rheology over a 24-hour press run.

UV offset inks must maintain stable ink-water balance and minimize misting at high-speed press operation (15,000+ iph). High-MW oligomeric mistabilizers and modified silicone additives reduce misting without affecting cure. Special wetting agents balance interfacial tension between ink and fountain solution. The fountain solution itself uses UV-compatible additives to prevent emulsification breakdown over long runs.