Processing and application of uv curable powder coatings

The process of manufacturing UV powder coatings is not very different than the process of regular powder. The process only differs in the extrusion temperature and the addition of photoinitiator with UV powder systems. A more detailed description of processing and application will be described below.

The mixing of the ingredients for the coating is done with a grinder. The resulting premix is a fine powder that contains all the components of UV powder coatings. This powder is only mixed at macroscopic level.

In order to mix the components at a molecular level the premix is extruded. UV-curable powder coatings can be manufactured using standard extruders. The ingredients are mixed via melt-extrusion under normal conditions. The extrusion temperature must be high enough to liquefy the powder, but not too high - otherwise the powder will melt in the extruder. As the UV-powder coating is designed to flow at a relatively low temperature of 100°C, the melt viscosity of the UV powder is much lower than a thermoset powder coating system. Therefore, the extrusion should be performed at a temperature of 70°C. At this temperature the binder system allows for standard processing in a conventional powder coating manufacturing process. The temperature of the extrudate should not exceed 75°C. Heat development in the extruder can lead to higher temperatures than the setting temperature of the extruder.

After the extrusion, the extrudate needs some time for recrystallisation (at least 2 hours depending on the processing parameters). After the recrystallisation the extrudate can be ground.

First the powder particles are ground with a mill with holes of 0.5-1.0mm and then sieved with holes of 90µm. The resulting fine powder has a size of <90µm.

To store the powder coating for an extended time, it is advisable to store the powder under dry and dark conditions. The formulations given in the next chapter are stable at 30°C for four weeks. The UV powder coating is chemically stable during storage because polymerization will only be initiated by UV radiation.

The application of the powder particles to the substrate can be done with a conventional spray system. Application of UV powder is no different than conventional powder coating techniques. Corona is used for metal substrates. Except when thick layers are preferred it is better to use a tribo gun. For MDF substrates the tribo gun is used to apply the powder particles.

Application of UV powder coating with a
manual spray gun (corona) on a metal
substrate.