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Dacrylate Paints Ltd.

Coating Curing Methods

Curing Methods

Some coatings require the application of some form of additional energy to cure the film or to speed up the rate of cure to acceptable production rates. It is possible to fully cure certain coatings in seconds, giving extremely high line speeds for such items as domestic doors.

Convection Curing

If the painted items are placed within the confines of an oven, the extra energy transmitted to the coating will speed up the curing process enormously. Coatings that typically take 8 hours to through dry can be cured in 20 minutes or less at a temperature of 120°C.

The energy transfer takes place by conduction, the heated air molecules give up a portion of their energy to the (usually) metal which slowly heats up to match the air temperature. Large metal masses eg castings absorb huge amounts of energy before equalizing with the air temperature. It is important that when setting or following recommendations for stoving conditions, that it is understood that the temperature quoted on information sheets is that of the metal, not of the air. A heavy casting placed in an oven set at 120°C can take an appreciable time to reach that temperature (sometimes several hours!) and the paint film temperature will rise at roughly the same rate as the metal temperature.

Infra-Red Curing

The coated articles are passed in front of a series of infra red panels, which can be either gas or electrically powered. The energy is transmitted as radiant energy (as a domestic grill) and travels in straight lines only. It is essential that parts of the object are not shielded by any other part, as they will receive less energy and be under-cured. To help overcome this effect, the panels are usually arranged in front of a curved polished reflector to re-direct any radiation that misses the object.

Dacrylate Infra Red Paint CuringBecause of the high energy levels, short curing times can be achieved. As the energy is transmitted by radiation, there is no heating of the surrounding air or the substrate up to curing temperature, which enables much shorter curing periods (typically 10 minutes) to be achieved. As the heating takes place as a surface effect, the method is more suitable for heavy fabrications than convection.

Dark colours absorb infra red radiation better (and hence cure faster) than do pale colours, (the reason why black objects get hotter than white objects in the sun) and matt finishes absorb more than glossy finishes.

UV Curing

Usually associated with clear or transparent finishes, mainly applied to wood or paper substrates. Intense UV light is focused on the coated objects, usually flat panels. Extremely fast cure speeds can be achieved (down to seconds) therefore very high line speeds can be utilised.

Electron Beam Curing

Intense beams of accelerated electrons are focused on the painted substrate, usually flat panels. Curing can take place in fractions of a second. The system is almost invariably used for wood finishing. The system is extremely expensive and therefore suitable only for mass production.

 

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