Curing of powder coatings with UV light can be described as "the best of two worlds". This new method makes it possible to benefit from the advantages of high cure speed and low cure temperature as well as environmental friendliness.
The handling and preparation of UV powder coatings is similar to the methods used for conventional powder coatings. During application the UV powder coating is generally melted by exposure to IR light. This process takes only 1-2 minutes with a required final temperature of 90-140°C, depending on the selected UV powder system.
Because of this relatively low temperature it is possible to cure heat sensitive substrates with UV powder such as MDF, plastic, glass and pre-assembled parts which combine metal and heat sensitive materials.
UV powder can also be applied on metal, with the main advantage that the metal does not have to be heated to such high temperatures, or for as much time as required with thermal curing powder coatings.
Crosslinking of the melted UV powder occurs by exposure to UV light. The curing by UV radiation is only a few seconds which gives a total curing time of 1-3 minutes.
The cured coating has properties of adhesion and hardness that compare very well to liquid UV coating and the chemical resistance is generally even better.
UV curable powder coatings are very environmentally friendly for several reasons. First, there is hardly any emission of volatile organic compounds. In the future it is expected that the emission of VOC´s from industrial processes will be decreased and controlled by governmental regulations. As a result many companies will have to decrease their emission of VOC´s drastically. The use of UV curable powder is a good solution.
Another factor affecting the environmental friendliness is the much shorter heating period compared to conventional powder, as well as the lower heating temperature. UV curable powder coating saves energy and reduces CO2 emissions. Compared to solvent based systems the waste of UV powder coating is much lower because overspray is easily reclaimed and reused.
The total costs of a coating system depend very much on the costs of the material used. In general, UV powder has the advantage of high material utilisation. 95% of the powder can be used, compared to 60% for most sprayed wet paints.
As mentioned above, the overspray of UV powder coating can be recycled , whereas overspray of liquid paints is generally scrapped. Therefore, the price per liter or kg of paint cannot be fairly compared.
Comparisons can better be based on the price per coated square meter. The price per coated square meter is also dependent on the number of coating layers. A good result with UV powder coating is often obtained with one layer. With other coating systems, such as UV liquid or nitrocellulose lacquers, multiple layers are necessary, which increase the costs per square meter.
The main advantages of UV curable powder systems are:
The handling and processing of the powder is much like the handling and processing of conventional powder and a standard extruder can be used.
Source: DSM Coating Resins
Powder Coater's Manual 1/98
August 28, 2006