Development of New Bonding Technologies for Powder Coatings
Abstract
The metallic effect powder coatings (MEPC), composed of regular powder coating materials and metallic pigments, share an increasing market because they provide an aesthetic metallic effect and also enhance protection. Mainstream industrial production employs a thermal bonding technology to incorporate and immobilize the metallic pigments to coating particles. However, a series of inherent shortcomings of the thermal technology have affected the promotion and deployment of MEPC, such as mis-bonding, metallic flake deformation, inability for high-temperature bonding, etc. To address these issues, cold, single-component-heating (SCH) and microwave bonding methods have been proposed and tested in this thesis work.
The cold and SCH bonding methods both were shown to have enhanced bonding quality and small Al-content relative difference of less than 5%, but could not compete with the microwave bonding method that has high heating rates and easy real-time control, and is more readily for industrialization. A thorough study on the microwave bonding method from lab to industrial-scale experiments provided a comprehensive understanding of the process and mechanism of microwave bonding including the bonding quality and color stability. Microwaves exhibited significant advancements in heating rate (10-23°C/min), which enabled a much higher production efficiency and a lower energy consumption than the current bonding technology. In the microwave bonding, the temperature of particles is easy to control. Furthermore, the bonding quality increased by 100% and the color is much more stable compared to the current commercial method. Based on solid experiments and reliable results, the microwave bonding devices have been scaled up from lab-scale (0.05 kg/batch) to pilot-scale (10 kg/batch) and finally to industrial-scale (100 kg/batch). The industrial microwave bonding machine successfully overcame the shortcomings of the current commercial bonding machine, and achieved better bonding quality and more stable color with higher productivity and less energy consumption.
In conclusion, the microwave bonding method shows obvious superiority over the current bonding technology, as well as the cold and SCH bonding methods studied here. It avoids the current shortcomings of bonding, provides better bonding quality and color stability, and achieves higher production efficiency. The industrial-scale microwave bonding machines are expected to replace the current bonding machines in the very near future.