Curing of the powder coating (Topic: 14087)

The curing operation is carried out in curing ovens. A curing oven should:

1 Be energy efficient.

2. Have the same temperature across the length or the height of the extrusion.

3. Not have too much turbulence, so that powder isn't blown away.

The two last conditions are contrasting, as uniformity of temperature is often obtained by strong air recirculation. This means that air speeds in the oven must be well calculated.

The energy required for the curing operation is given by supplying heat in two different ways:

- hot air convection heating

- IR (infra-red) -radiation

Some producers of powder coated profiles use both hot air convection heating and IR-radiation. The IR-elements are placed in the entrance of the curing oven in order to give a rapid and effective energy transfer in the melting reaction of the powder coating, thereby minimising the chance of powder being blown off.

Normally the temperature to get proper curing of a powder coating is around 200ƒC, and the curing time may be 10ñ15 minutes.

To obtain a powder coating with good level or flow properties - that means without any orange peel - the temperature has to be at the correct level at the entrance of the oven to ensure a proper melting of the powder. After melting, there is a reaction between the resin and the crosslinking agent, and a chemical bonding takes place between molecules. This is the reason for the good wear resistance and surface hardness of the thermosetting powder lacquers compared with the thermoplastic powders, where only a fusion of powder particles occurs during the curing reaction.