BUBBLE DEFECTS AND CONTROL OF THERMAL CURING OF WATERBORNE RESIN COATINGS

To solve the problem of bubble retention leading to a decrease in the performance of waterborne resin coatings during thermal curing, a rapid thermal curing coating based on an aqueous epoxy-modified acrylic resin containing an amino resin cross linker was synthesized through solution copolymerization. Using a synchronous thermal analyzer, the mass loss and heat flow during the thermal curing process of the coating was measured. In addition, an in situ thermal curing visualization system was used to observe the curing behavior at the easy-open end notches under different heating rates. The results indicated that the curing process is divided into an initial rapid heating stage and a subsequent slower heating stage by the boiling point of water, with a critical temperature range of 126-150°C. The visualization experiments showed that when the temperature reached 100°C, the water quickly evaporated to form bubbles. Increasing the heating rate before this temperature caused the bubbles to rapidly escape. Therefore, an optimal heating profile with a rapid initial heating rate of 3.13°C/s, followed by a slower heating rate of 0.52°C/s in the next stage, is proposed. This discovery is of great significance for optimizing the thermal curing process of waterborne coatings on metal substrates, including those used for easy-open ends.