Quality Evaluation of Coated Film Quick Dried by Far-Infrared Radiation

Abstract Reduction of the drying time for sprayed coatings is one of the critical issues in shipbuilding and offshore industry to increase their productivity. So, accelerated drying of the sprayed coatings has been widely used and new techniques to speed up the drying stage of the sprayed coatings have received considerable attention in the related industry. Infrared drying method has significant advantages over conventional one, because the thermal radiation emitted from infrared source is more readily absorbed into the bulk of the coating, with less temperature gradient in the coated film. The drying time of the coating system may be dramatically reduced if far-infrared radiation, having similar characteristic frequency with the coating material itself, is irradiated on the coated surface. This phenomenon, the sudden increase of the vibration energy of coating moleculars, can be explained as Absorption / Resonance response of the coating system by far-infrared radiation. In this study, to evaluate the effectiveness of far-infrared drying method on the pipe coating process, various tests such as adhesion, flexibility, impact resistance, cupping as well as salt spray test, were carried out to compare the physical properties and the drying characteristics of the coating systems under either natural or far-infrared radiation drying condition. The results clearly indicated that coatings with shortened drying time by the far-infrared radiation revealed same physical properties and quality of the coating as those dried by natural drying method. From these results, it is suggested that the productivity of the overall coating process for the pipe pieces in shipbuilding and offshore industry can be increased by adopting an accelerated drying method, such as far-infrared radiation without sacrificing the coating quality.