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Coatings protect surfaces, provide them with new functions and refine them with special colours and haptic elements. UV coatings with environmentally friendly properties are becoming increasingly popular: Since nearly all of their components react with each other during the UV curing process, hardly any VOC emissions are produced when they are processed. That makes them a particularly interesting alternative to solvent-based coating systems, which are the subject of growing regulatory scrutiny.
UV coatings are applied using a rolling or spraying process. They are dried using sources of radiation that emit ultraviolet light and do not require a lot of heat. The photo initiators contained in the coating absorb the energy from the light and disaggregate, which triggers a chain reaction – following a short, high-energy radiation, the UV coating systems are cured. The advantage: The coated substrates can immediately be processed further, packaged or stacked. That results in an increase in productivity in the manufacturing sector.
“UV systems are mainly used on flat surfaces,” said FreiLacke’s Dipl.-Ing. (FH) Beate Brehmer. “But the development of 3D curing mechanisms is progressing rapidly, which means they can also be used on less even surfaces. As a result, we are seeing an increased use of hydro UV coatings”. The former are usually applied as UV spray coatings in order to minimise solvent emissions in the production process. If the surfaces are flat, completely solvent-free UV coatings can be rolled on.
The coating expert Frei offers a variety of UV coatings that stand out because of their very short curing times and very good mechanical resistance. For example, immediately after they are fully cured, the ES1910, ES1952 or ES1913 UV coatings feature a surface hardness of more than 100 oscillations according to the pendulum hardening method. “This is also evidenced by the abrasion test according to TaberAbrasor CS10 2 x 500 gram at 500 revolutions. The abrasion of the FreiLacke products ES1901 and ES1952 is less than 5 milligrams”, explained Gut. In comparison: It is approximately 10 to 15 milligrams for conventional UV coatings.
Thanks to its integrated nano particles, ES1952H in particular boasts a very high scratch resistance, good elasticity and good chemical resistance, which was tested in accordance with DIN 68861, according to the coating expert. In addition, the ES1910 and ES1913G systems also feature top chemical and disinfectant resistance, which customers often demanded for interiors.
Over the past decades, UV coatings were primarily used for wooden surfaces. But that has changed: They are now also being used for substrates like metal or plastic. But UV clear coatings from FreiLacke do not just protect surfaces: Systems like ES1975HF or ES1970 are also well suited as adhesive primers on difficult substrates prior to printing in order to ensure the adhesion of digital print colours.
The demand for digitally printed surfaces with UV materials is also on the rise – for example for plastic substrates in construction, walling elements for interiors and sanitary facilities as well as for printed outdoor industrial surfaces. That is also the case at Stengel GmbH from Ellwangen: The company specialises in the production of metal tiles for the shipbuilding sector – in particular for wet rooms. Stengel has been relying on UV systems from FreiLacke since 2013. “First, we prime our metal tiles with a white UV basecoat using a spraying application. Following the partial gelling, the tiles are placed in large flatbed printers, where the decorative UV coating is applied”, explained Uwe Sendner, the head of production. Both layers are dried using special UV lamps and then receive an overcoat of protective clear coating that is sprayed on. Another production process is not worth considering, according to Sendner, because the quality is just right and the workflow has been perfected. Stengel and FreiLacke are currently jointly researching an anti-slip coating for ships.
UV-curable coating systems largely consist of oligomers (binding agents) and monomers (reactive thinners). They are primarily responsible for film formation and give the coating system its basic properties. The monomers are also tasked with reducing the viscosity. It is essential that the formulation contains photoinitiators in order to initiate radical polymerisation. Fillers and pigments can be used for providing colour and matting as well as to keep prices low. Classic additives improve defoaming, flow, wetting and light protection.
Depending on the applications process, the layer thicknesses of the UV systems of the coating manufacturer from the Black Forest vary from 10 to more than 80 micrometres. That allows them to meet a wide range of gloss levels from high gloss (angle < 20°:70-90GE) to matt (<60°: 15GE). Following 1,000 hours of WOM weathering, the products ES 1901, ES1970 and ES1952 feature a residual gloss of >90 percent and a dE value of <1.5. In addition, FreiLacke has developed some highly matt systems in recent years that were well received by customers.
