In the recent years, thermoset powder coating has been overgrowing as a clean and environmentally friendly technology to respond increasing demands of environmental legislation and global regulatory attention for reducing Volatile Organic Compounds (VOC) in the coatings industry. It uses 100% solid components formulation including resins, pigments, fillers, curing agents, and other additives. Resins usually determine the properties of the coating such as abrasion resistance, corrosion protection, adhesion, and weatherability.
Based on the resin or binder used in the powder coating, there are two coating systems: thermoplastic and thermoset. UV-powder coating was developed to achieve low-temperature thermoset curing. Incorporation of both powder curing and UV technologies provides rapid cure at lower temperatures which is suitable for heat-sensitive substrates like wood or plastic. In the UV-powder coating, the melt flow process is separated from the curing. When the coating applied on the substrate, it will be heated to the melt; then, cured by the UV light. Since the melt temperature is lower than usual, conventional cosmetic problems such as orange-peel effect and poor leveling are minimized in the UV-powder coating.
In the present study a UV-curable bismaleimide methacrylated polyimide (BMI-PI-MA) was synthesized and fully characterized. BMIs are classified as thermoset polyimides (PI) with two maleimide end groups. These resins can do either thermal or UV curing. BMIs have high Tg, high thermal stability, high chemical resistance, and excellent mechanical properties. Synthesized BMI-PI-MA was mixed and formulated at different contents with a commercially available resin, UVECOAT, to study the application of UV powder coating. Resulted blends have shown the formation of polymer networks at the molten state and under UV light. Properties of UV cured films were investigated by thermomechanical analysis (TMA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). In addition, SAOS and LAOS rheological studies have provided further details when UV-cured films subjected to different strains. The results showed that addition of BMI-PI-MA to the formulations can improve the properties of the UV-curable powder coating at the certain levels.