HIGH-INTENSITY INFRARED DRYING STUDY .2. CASE OF THIN COATED FILMS

This study describes the combined drying (convective and infrared) of aqueous coated films under high infrared densities (i.e. 5-18 kW m-2). This shrinking, highly hygroscopic and transparent material exhibited specific characteristics which are very different to those observed i n a pure convective drying process. Thus, the strong influence of the radiative properties of the support (absorptivity, reflectivity) on th e drying kinetics and on the film temperatures of the material was obs erved. Modelling of the drying process, based on a diffusional model w ritten using a mobile frame of coordinates (Lagrangian coordinates) an d associated with an overall heat balance in the support + coated film system, has proved capable of expressing the drying curves and temper ature evolution very precisely. Before simulation, two main coating pr operties were deduced from drying experiments: (i) the mean absorptivi ty as a function of the mean moisture content, and (ii) the apparent d iffusivity as a function of the temperature and of the local moisture content. So, this simulation lets us approach quantitatively the proce ss control and the risk of bubbling (or swelling) during the final dry ing period.