What is the Powder Coating Process?
Powder coating is a type of polymer coating that is applied as a free-flowing, dry powder and the fused or cured to give high performance paint like layer.The main difference between a conventional liquid paint and a powder coating is that powder coating are 100% solids and do not use volatile solvents or thinners.The powder coating is typically applied using electrostatic charge and is then cured under heat to allow it to flow and form a plastic like polymer covering
Powder Polymer Coating is classed as either:
Thermoplastic polymers can be melted and remoulded they are polymers that turns to a liquid when heated and then solidify to a hard coating when cooled The thermoplastic type do not undergo any additional chemical reactions during the baking process, but only flow out to produce the final coating.
Thermoset powders are polymer materials that irreversibly cure by application of heat and temperatures typically from 160 to 200 degrees Celsius. They cannot be melted and remoulded after curing. When the powder is baked, it reacts with other chemical groups in the powder to polymerize, improving the performance properties.
Polymer Resin Types
The most common polymers used are polyester, polyurethane, polyester-epoxy (known as hybrid), straight epoxy (fusion bonded epoxy) and acrylics.
Powder Coating Process
Powder coating is a method of applying a decorative and protective finish to a wide range of materials and products Powder coating create a durable finish that is much tougher and harder than conventional liquid air or forced dried paints. Powder coating process is one of the most advanced coating processes available offering finish durability and longevity. The powder coating process involves electrostatically charged resin and pigments that are sprayed onto an electrically grounded surface. Colour selection is virtually unlimited with high and low gloss finishes available. Texture selections range from smooth surfaces to a wrinkled or matte finish, and rough textures designed for hiding surface imperfections.
Powder coating is mainly used for coating of metals such as
White goods and major household appliances such as washing machines, dish washers, tumble driers, air conditioner, microwave ovens , fridges, and freezers
Household appliances and parts
Small appliances parts, trim and covers for: computers, laptops, TV, CD and DVD players, camcorders, still cameras, clocks, alarm clocks, video game consoles, Hi Fi, home cinema, mobile phones, cameras, camcorders telephones and answering machines.
Metal parts and furniture such as: jewellery, garden furniture, sports goods, kitchen chairs, door handles, locks and hard ware
Parts for automotive applications, car, van, truck, motor bikes, bicycles, wheels, trim, engine components and fixing.
Aluminium extrusions and die casting for office or retail furniture partitioning and trunking systems,
In fact almost all metal part can be powder coated the only real limitation is heat sensitive substrates or very small parts.Newer technologies allow other materials, such as MDF (medium-density fibreboard), to be powder coated using special methods
Powder coating versus conventional liquid coatings:
Main advantages of powder coating over conventional liquid coatings:
1. Powder coatings release zero or near zero volatile organic compounds (VOC).
2. Powder coatings can produce much uniform coatings than conventional liquid coatings without running or sagging.
3. Powder coating overspray can be recycled and in theory achieve nearly 100% use of the coating.
4. Powder coating production lines produce less hazardous waste than conventional liquid coatings.
5. Capital equipment and operating costs for a powder line are generally less than for automated conventional liquid spray application lines.
7. A wide range of specialty effects such as metallic hammer finish are easy to do
When a thermoset powder is exposed to elevated temperature, it begins to melt, flows out, and then chemically reacts to form a higher molecular weight polymer in a network-like structure. This cure process, called crosslinking, requires a certain temperature for a certain length of time in order to reach full cure and establish the full film properties for which the material was designed. Normally the powders cure at 200°C (390°F) for 10 minutes. The curing schedule could vary according to the manufacturer's specifications.
The application of energy to the product to be cured can be accomplished by convection cure ovens or infrared cure ovens.
Powder Application Processes
Example powder coating spray guns
Electrostatic or Corona gun
Type of gun called a tribo gun is a spray gun which charges the powder by (triboelectric) friction. In this case, the powder picks up a positive charge while rubbing along the wall of a Teflon tube inside the barrel of the gun. These charged powder particles then adhere to the grounded substrate. Using a tribo gun requires a different formulation of powder than the more common corona guns. Tribo guns are not subject to some of the problems associated with corona guns, however, such as back ionization and the Faraday cage effect.Fluidized Bed Electrostatic Discs.
Powder can also be applied using specifically adapted electrostatic discs.
Another method of applying powder coating, called the fluidized bed method, is by heating the substrate and then dipping it into an aerated, powder-filled bed. The powder sticks and melts to the hot object. Further heating is usually required to finish curing the coating. This method is generally used when the desired thickness of coating is to exceed 300 micrometres. This is how most dishwasher racks are coated.
The powder coating process is environmentally safe. There are virtually no VOC's (Volatile Organic Compound) released during the application and curing of the powder.