Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE The drying behavior of a two-component polyurethane coating on aluminium plates is investigated under conventional, infrared, and hybrid heating using image processing-based color change (ΔE) analysis alongside temperature and weight measurements. The ΔE plateau closely tracks the touch-dry state, enabling contactless real-time monitoring. Hybrid drying yields the most stable optical quality, while infrared drying achieves the lowest energy consumption.

ABSTRACT
In this study, the drying behavior of aluminium surfaces coated with polyurethane coating was investigated using conventional, infrared (IR), and hybrid (conventional + IR) drying methods. The drying process was evaluated using temperature, weight loss, and image processing-based color change (ΔE*ab, CIE 1976) analyses. The results showed that conventional drying was slow and spread over time, IR drying caused rapid color change on the surface in the initial stage, and hybrid drying offered a more controlled temperature distribution, stable weight loss, and more balanced color change behavior. Quantitatively, the ΔE plateau levels were found to be 6.0–6.3 for conventional drying, 4.2–4.5 for IR drying, and 3.7–4.0 for hybrid drying, while the energy consumption until touch-dry time was 0.303, 0.112, and 0.359 kWh, respectively. The color change and weight loss profiles were mutually consistent throughout the drying process, both exhibiting a rapid initial change followed by gradual stabilization, with weight loss slightly preceding color stabilization. This reflects the progression from surface solvent evaporation to internal diffusion-controlled drying. The image processing-based approach enabled continuous, contactless monitoring of the drying process and has been shown to complement traditional temperature and weight measurements.