The curing with UV light is a photochemical process using high-energetic UV radiation for cross linking of coatings or adhesions. For studies on UV-reactive systems we use a Light Hammer 6 made by Fusion UV Systems.
The main field of application of UV curing are the wood-working industry and the furniture industry, as well as the printing industry. Aside of this there are several other areas, like suppliers for car manufacturers (head lights) and the production of CDs, DVDs and Blu-ray discs. Beacuse of the very fast reaction mechanism the speed of processes is very high. After the very short exposure time the coated or glued objects can continue processing, can get stacked or packed. Because of the very short-term application of energy the temperature of the objects raises only slightly. This minor temperature raise is beneficial for temperature-sensitive substrates like plastics and wood. Threw wisely selection of the right primary products it is possible to produce a solvent free product, complying environmental specification (VOC) and saving energy, which normally is needed for evapourating solvents and heating of the objects. Which also saves spacious drying areas.
Beside these positive procedural aspects, the resulting coatings show positive characteristics: They show a very high scratch resistance (scrub resistance) and chemical resistance. Additionally high degrees of gloss can be achieved.
Beside all positive aspects there are also some negative issues worth considering: The initiator molecule gets activated within a particular wavelength range. Therefore it is essential, that the formulated coating systems (e.g.: pigments, additives like UV absorbers) won't absorp radiation inside this wavelength range. For optimum curing initiators and used UV lamps must be coordinated. The coated subjects may have no shadow zones. Where the radiation can't reach sufficiently, there won't be any physical drying, leaving a wet film. By dispensing of solvents low molecular weight substances are used to adjust the viscosity, which are incorporated into the molecular network. However these monomers, oligomers or prepolymers mostly have health and procedural aspects, that need to be taken into account. As with any system change, the transition to UV coatings, the familiar properties (e.g. grain enhancement with wood, adhesion to metal) need to be regained.
At the University of Paderborn new ideas in the field of UV coatings get developed with the help of an UV tube. In addition, the device is also used as a basic tool e.g. to "freeze" liquid crystals for the analysis of anisotropic behavior in paints. In addition, the equipment offers our students the opportunity to learn practically the UV curing.