Powder coatings are paints in powder form. Chemically curing resins, such as epoxy polyester, acrylic and polyurethane, are used as powder coatings. Powder coatings are mainly used for product painting in the metal industry. The powder coating process is very similar to a painting process except that the “paint” is a dry powder rather than a liquid.
Typical objects are light fittings, domestic appliances, furniture, and bicycles. Powder coatings are generally applied by electrostatic spraying. The powder adheres to the metal item, which is connected to earth. The final coat is formed by a chemical reaction at a temperature of 150 -200°C.
Powder coatings form a tightly adherent, mechanically and chemically resistant surface. Polyamide, polyethylene or polyvinyl chloride is used as resins for thermoset powder coatings. The powder is spread over the surface by a floating method and it forms a film when heated, when the powder melts and sticks to the substrate.
The powder sticks to the parts due to electrostatic charging of the powder and grounding of the parts.
Any substrate can be used that can tolerate the heat of curing the powder and that can be electrically grounded to enhance charged particle attachment. The powder flows and cures during the application of heat.
Several advantages of powder coating over paints are:
Powder recovery for reuse
No VOC generation therefore no VOC destruction required
Can be more durable than paints (powder chemistry dependent)
Several disadvantages of powder coating over paints are:
Can have less leveling than paint
Curing is typically more energy intensive than paint drying due to higher temperature requirements
Surface preparation before powder coat application is still critical for adhesion and defect avoidance.
Typical steps in a powder coating process for metal parts:
1. Cleaning (typically an alkaline cleaner, but substrate dependent)
3. Phosphating (optional step to improve corrosion protection and adhesion)
5. Powder Coating
6. Curing (typically energy intensive since relatively high temperatures are required to get the powder to liquefy and flow)
For more information, please visit http://www.samaterials.com/406-thermal-spraying-material