Drying Of Organic Coatings by Infrared Radiation of Different Wavelengths

Beside the environmental aspects, the use of infrared radiation for waterbased
paints meets the requirement of reducing the time and energy needed for the drying
procedure. Thereby is expected a high efficiency of converting electrical energy into
radiation energy. Only the surface region should be heated to the required
temperature and the bulk should stay on a lower temperature level. Because of the
short reaction times of the emitters, continous in time" heating of complicated,
convex bodies with different distances between the surface and the radiator can be
realized. For the energy transfer to surface areas not directly irradiated and for
removing the water vapour convectional drying is mostly used additionally.

In practice, the measurement of all quantities characterizing the drying process
(surface temperature, irradiation, mass fluxes of all the molecule species contained
in the liquid coating, carrier gas velocity e.g.) is not possible. Experiments in the
laboratory are also difficult from the technical point of view and yield an enormeous
amount of data because of the high number of experimental parameters and different
binder-solvent-pigment combinations.

The recent development to waterbased UV-curable paints exhibits beside the well
decribed advantages 1] one inherent disadvantage: the water has to be removed
completely before exposure to UV radiation. The infrared drying technique can be
adapted to the UV curing as pretreatment process, because the chemical nature of
the most important constituents of the UV curable systems (water, resins, solvents)
are similar to the conventional waterbased coatings. But special attention has to be
drawn to the possible loss of photoinitiators and accelerators during the IR drying
1,2].

This paper presents in section 2. a short technical review of a equipment for
measuring the drying kinetics of.waterbased coatings, solvents and blends. Section
3. concerns with the drying of pigmented waterbased coatings by using radiators of
different emission spectra. Then follow in section 4. some results on the evaporation
of water-amine blends.