UV Curing

Photosensitive resins and polymers used in UV curing rely on photoinitiators that absorb ultraviolet photons and undergo homolytic or heterolytic cleavage to generate reactive species, most commonly free radicals or cations, which then initiate polymerization.

In free-radical systems (e.g., acrylates), Type I photoinitiators like benzoin ethers or acylphosphine oxides fragment upon UV exposure to directly release radicals, while Type II initiators such as benzophenone abstract hydrogen from co-initiators like amines to form radicals; these species attack carbon–carbon double bonds in the resin’s monomers and propagate crosslinking.

In cationic systems (e.g., epoxides), diaryliodonium or triarylsulfonium salts release strong Lewis acids upon irradiation, producing cationic centers that trigger ring-opening polymerization.

The rapid buildup of covalent bonds between monomers transforms the liquid resin into a rigid, crosslinked solid, with polymerization depth and mechanical properties governed by initiator concentration, UV wavelength, and resin formulation.