Q: I carry out jobbing, currently doing batch oven curing. I understand that UV powder coating materials are different, but what will be the temperature required for the first stage of melt? After this, can the parts be touched before transferring to the UV curing?
Are UV powders more expensive than normal epoxy powders? How about the energy costs? Can you give some insights about UV-cured powder coatings? How is this process carried out?
A: Indeed, the powder must be melted, and it cures best at an elevated temperature. The melt phase can be accomplished by any source of heat: convection, infrared, or a combination of both. This can take anywhere from a few seconds to a minute or two depending on the source and the intensity of heat.
The melt temperature depends upon the formulation and can range from about 100°C up to 125°C (212- 257°F). The parts can be touched, but the coating should not be touched.
UV powders are generally more expensive than epoxies, but not outrageously so. Energy costs are quite low, though the process is more complex. Heating a substrate to 110°C instead of 180-200°C obviously saves cost. The UV process requires high energy, but it is very compact and saves floor space and capital equipment expenditure.
UV cure is “line of sight,” meaning the UV energy must penetrate the coating. Shadows and unexposed spots do not cure. The UV curing typically takes seconds, very few seconds. Too long and the coating will burn. In addition, it is important that the coating is warm and relatively fluid when exposed to the UV energy. This allows for better molecular mobility and more complete cure.
Any substrate that can be powder coated can most probably be coated and cured with a UV powder. The key is to melt the powder without damaging the substrate. Metal substrates are relatively easy to finish with UV powders. More difficult are plastics, especially those possessing low heat distortion temperatures (HDTs).