Powder coatings are only semi-finished products; they only become finished products after spraying and curing. Consumers focus on the effect and quality of the coating after application. In other words, using powder coatings is just as important as producing them. Low-quality powder, no matter how good the spraying equipment, how meticulous the pretreatment, or how strict the coating process, will not produce a high-quality product. Conversely, even with high-quality powder, problems with the spraying equipment, process, or pretreatment will also result in a low-quality product. However, in reality, most domestic coating companies focus on the powder coating product itself, only blaming the powder when quality problems arise, while neglecting the importance and research on coating application techniques. This leads to a large number of coating products failing to achieve the desired effect.
Each powder coating has its own curing characteristic curve, which can achieve complete curing within a certain temperature and time range. Violating this principle by shortening the curing time to improve efficiency and reduce costs is unacceptable. If the curing temperature or time is insufficient, incomplete curing will occur, preventing the coating from achieving its intended performance. Its physical properties will be greatly reduced, chemical resistance will be poor, and its decorative, corrosion-resistant, and weather-resistant properties will not meet expectations. Even after complete curing, some low-temperature cured coatings do not perform as well as high-temperature cured coatings. This is especially true for some workpieces that have been cured and formed; fine cracks can form at stamping and bending points, allowing moisture to seep in and quickly corrode the substrate. We can see this in outdoor traffic grates, which develop rust at the curved corners of intersections shortly after installation. This is directly related to the baking temperature and time, as well as bending after spraying.
Some people believe that lower heating temperatures reduce the reaction rate and improve leveling. However, the opposite is true. After powder coating, melting and curing occur almost simultaneously. Rapid heating and a fast temperature rise cause the system viscosity to decrease rapidly, completing the leveling process before gelation. This results in good leveling properties and less orange peel. Simultaneously, the coating effectively wets the surface, improving adhesion and durability. While rapid curing may increase internal stress in the film, the thinness of the coating minimizes the impact on physical properties. Conversely, if heating is slow, the system viscosity remains consistently high. At this point, curing has already begun, and the viscosity continues to rise as the reaction progresses, resulting in poor leveling.
In short, to achieve ideal coating results and long-term protection, heating should be rapid to reach the curing temperature in a short time. However, if the heating temperature is too low or the heating time is too long, curing will occur before the powder coating melts, levels, and wets the substrate, leading to unsatisfactory physical properties. Furthermore, volatile substances are difficult to escape, causing premature damage to the coating under corrosive conditions, thus failing to achieve both decorative and protective properties.