UV-Curing Pack Systems for Complex Plastic Parts
Reduced Environmental Impact Compared to Solvent-Containing Paints
Plastic parts for automotive interior applications are increasingly being coated with high-gloss paints. As a rule, these are usually solvent-containing 2-component paint systems. Drying and thermal curing of these paints involve relatively high energy consumption. Until now, UV-curing paint systems could be used to only a very limited extent on plastic surfaces, since exposure to heat adversely affected the dimensional stability of the plastic parts.
For this reason, new paint systems which produce a scratch resistant surface coating on the plastic and are based solely on UV-induced curing of the paint coating at low UV power densities have been developed in a research project. By varying the photo- initiators, reactive thinners and oligomers used in new formulations, it has been possible to achieve full cure at a low UV power density and low dosage. Until now, UV-curing paints in these applications required a dosage of 1.5 to 2 J/cm² in conjunction with an intensity of the 0.7 to 2 W/cm² for a defined full cure. The results achieved show that even with lowering of the UV intensity by 50 to 90 % and a reduced UV dosage stable process windows can be found.
Replacement of solvent-containing paint systems with UV-curing paints for high-gloss applications on plastic surfaces offers great potential for reduced environmental impact. Reducing VOC emissions from the paint contributes directly to mitigation of climate change. In addition, the use of UV-curing systems can significantly reduce the amount of energy required, since thermal drying and cleaning of the exhaust air are no longer needed. The material efficiency aspect is particularly serious. With UV-paints, the material that does not reach the part, but instead ends up in the surroundings as spray mist (overspray) can be reused – this is not possible with standard 2-component paints. This alone can result in reduced pain consumption by up to 60 %. In addition, the reject rate is lower. (hs)
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