Development of new UV LED curable inkjet varnishes

We have prepared three UV curable varnishes for inkjet printing that can be cured by UV LEDs (365–395 nm). The advantages of UV LEDs compared to medium pressure mercury lamps (conventional source of UV radiation) are lower energy consumption, possibility of immediate switching on/off, no IR radiation, no ozone generation and are mercury free. UV LEDs cannot effectively (or at all) cure formulations designed for mercury lamp curing. Developed UV varnishes enable the creation of special varnish effects on printed substrates (including 3D) thanks to partial curing with UV LEDs. Evaluated properties of prepared varnishes were viscosity, surface tension, reactivity, long-term stability and printability. The printing properties of prepared UV curable varnishes were tested on commercially available inkjet printing machine (Spotmatic 36, KOMFI). The cured varnish layers (thickness 20 and 40 μm) were evaluated in terms of mechanical properties (adhesion, elasticity) and optical properties (yellowness). Namely, the study of mechanical properties included the evaluation of adhesion by Tape test, quality of the varnish layer with respect to cutting and grooving, and elasticity/adhesion of grooved varnish layers after folding (180 °). Results showed that prepared UV LED curable varnishes have very good elasticity and adhesion to various printing substrates and enables further trouble-free mechanical processing of varnished products, such as cutting, grooving or bending.