While the UV systems technology and the appropriate chemistry have been developing continuously, the principle of irradiation curing has widely remained unchanged: High-energy UV irradiation causes chemical curing of UV reactive coatings within seconds.
The short-wave, high-energy UV irradiation in the spectrum between 200nm and 400nm is able to convert a liquid UV reactive substance into a solid film within a split second.
|visible light||780 - 380||1,60 - 3,26||adhesives|
|UV-A||380 - 315||3,26 - 3,94||deep curing||inks or coatings|
|UV-B||315 - 280||3,94 - 4,43||varnishes|
|UV-C||280 - 200||4,43 - 6,20||surface curing||sterilization|
|V-UV||200 - 100||6,20 - 12,4||absorption
for UV curing
Contrary to a thermal drying process, which works by evaporating the solvent contained in the coating, curing initiates a chemical reaction within the coating compound, which leads to a polymerization reaction.
As soon as the reaction is activated by the UV irradiation the ﬂuid layer “cross-links” to an inert flm within a split-second. The majority of UV coatings offer a 100% coating residual, i.e. they cure almost without loss of coat thickness or VOCemissions.
The irradiation-sensitive element of the coating formulation is the photo initiator. Inﬂuenced by the UV irradiation, the photo initiator - at a radical polymerization - forms free radicals, which are able to split the double bonds within the oligomeres and monomers. This is the start of a polymerization reaction, which transforms the ﬂuid varnish flm into a three-dimensional structure.