[China Aluminum Industry Network] Since its introduction in the 1960s, the electrostatic powder coating process has primarily been used for metal surface finishing. While many powder manufacturers and equipment suppliers have long claimed that this method can be applied to non-metallic surfaces, no industrial products have ever been successfully developed. However, in the late 1990s, with advancements in both powder coatings and spraying technology, it became possible to apply electrostatic powder coating to non-metallic materials. In recent years, companies like Yu Dong Gao Ting Shi and Eluda from the UK have focused on applying electrostatic powder coating to medium density fiberboard (MDF), achieving successful industrial production. This article explores these developments and aims to promote the growth of electrostatic powder coating technology in China.
1. Key Factors in Electrostatic Powder Coating Electrostatic powder spraying involves applying a powder coating using an electrostatic charge, followed by baking at a certain temperature. Several factors influence this process, including the object being coated, the type of powder used, the spray gun, and the baking equipment. Understanding these elements is crucial for optimizing the overall process.
2. Selection of the Object to Be Coated From an economic perspective, the choice of material to be coated depends on market demand. While metals are commonly used, wood and plastic are also viable options. Currently, plastics are not ideal due to temperature constraints. Wood, particularly MDF, is preferred because it can be made conductive through moisture control. As a hygroscopic material, wood absorbs and releases moisture, allowing it to maintain a balance with the environment. By adjusting its moisture content, wood can mimic the conductivity required for electrostatic powder coating. MDF, as a widely used eco-friendly building material, offers high-quality, consistent results and is well-suited for industrial applications.
3. Advances in Powder Coatings Thermosetting powders typically require high curing temperatures (around 180°C for 20 minutes), which limits their use. Recently, low-temperature curing powders have emerged, with some capable of curing at 120°C for 20 minutes. Although these powders still face challenges such as poor storage stability, ongoing research suggests improvements are on the horizon. In MDF coating, UV-curable and ultra-low-temperature powders are now used. For example, DSM has developed UV-curable powder coatings based on maleic acid and vinyl ether, suitable for MDF. Eluda, on the other hand, uses epoxy/polyester hybrid powders that cure at around 150°C, fitting within standard paint curing ranges.
4. Innovations in Spraying Equipment Traditional corona charging methods limited the application of electrostatic powder coating to metallic surfaces. However, new technologies such as Total Energy Controlled (T.E.C.) charging allow for more flexibility. This system automatically adjusts voltage and current based on the distance between the spray gun and the workpiece, maintaining consistent charging energy. This ensures better powder adhesion and application efficiency, even on non-conductive surfaces like MDF.
5. Baking Equipment Developments For ultra-low-temperature powders, specialized drying tunnels are used to eliminate volatile compounds from MDF under controlled conditions. These tunnels help stabilize the curing temperature and reduce emissions. Unlike UV curing, which uses infrared to melt the powder before UV light cures it in seconds, MDF curing often requires a combination of heat and time for optimal results.
Since the late 1990s, industrial production of electrostatic powder coating on MDF has begun. In August 1999, the UK launched the first fully automated MDF coating line. Looking ahead, the MDF dusting process is expected to grow rapidly over the next few years. Future improvements will include further development of low-temperature and UV-curing powders, diversification of coating types, and the use of TEC-charged spray guns combined with modified curing equipment. This will allow production lines to handle both metal and MDF materials. Additionally, we can expect other non-metallic materials to enter the field of electrostatic powder coating in the near future.
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