Customers today demand higher quality and durability from the products they buy. Not only do they expect these products to perform well; they want finishes to look good and resist corrosion for much longer periods of time. All finishing processes available through PPG Coatings Services, including powder coating, are designed to do just that.
Powder coatings are different from other types of coatings. Because they contain no liquids or solvents, they are the ultimate solution for environmental friendliness. As dry products, powder coatings also enable very high application efficiency because overspray can be easily reclaimed.
Powder coating materials are basically plastics that have been ground into a fine powder, which is then converted into a continuous film on a metal surface through exposure to heat. Formulated with plastic resins, pigments, flow agents and other special ingredients, powder coatings are mixed to achieve specific desired characteristics in the finished coating film.
Types of Powder Coatings
There are two basic classifications of powder coating materials: “thermoplastic” and “thermoset.”
- Thermoplastic powders are generally applied to a surface that has been preheated to a temperature significantly higher than the melting point of the powder. Using these products, the thermoplastic material is applied to a hot surface, which causes it to melt and “fusion bond” to the surface; then “flow out” into a strong, continuous film. As the film cools, the coating assumes its inherent physical properties, including the chemical and wear resistance for which thermoplastic powders are known.
Nylon powder coating materials are the most frequent type of thermoplastic powder manufactured type by PPG Coatings Services.
- Thermoset powders contain a heat-activated catalyst and are generally applied to a surface at ambient temperature. The surface and the powder are then heated and, as the temperature rises past the melt temperature of the powder (normally 250º-275ºF), it melts and “fusion bonds” to the surface. As the temperature continues to rise (normally 360º-380ºF) a heat-sensitive catalyst becomes active and causes the molecular structure of the plastic material to change or “cross-link.” The temperature is maintained while the coating material cures and forms a strong, hard, continuous film.
Although thermoset powder coating systems offer broad formulation flexibility, they are very durable and widely used by PPG Coatings Services for both decorative and functional applications.
Powder Coating Processes
Powder coating processes vary by the type of material being applied; however, they can generally be divided into four functions:
- Preparation of the surface
- Application of the powder
- Heating of the part
- Curing of the coating
Preparation of the surface starts with a process to ensure that the surface is properly cleaned and free of "soils" such as manufacturing oils. Subsequent surface treatments might include blasting, if required, and iron-phosphate or zinc-phosphate cleansing, depending on the desired long-term corrosion performance.
Thermoplastic powders normally require a primer to promote adhesion. Thermoset powders do not need a primer because they have a built-in adhesion promoter. Primers may be used with thermoset powders to enhance certain properties, but the associated priming material must be able to withstand the curing temperatures required for powder coatings.
Application of powder coatings at PPG Coatings Services involves two basic techniques with multiple variations for each. These two techniques are “fluidized bed” and “electrostatic spray.”
- The fluidized bed is the original – and still primary technique – for applying thermoplastic powders, although the process is also used to apply some thermoset powders where high film build is required. Thermoset powders designed for electrical insulation often use the fluidized bed technique. For these applications, parts are pre-heated to a temperature significantly higher than the melting point of the powder; then immersed in a “fluidized bed” of coating powder, where the plastic powder is melted onto the part.
- Electrostatic spray is the primary technique used for thermoset powders. This process begins when powder coatings particles are charged in a powder coating gun and the target part is attached to an electrically grounded fixture. Attracted to the grounded metal, the electrically charged particles attach themselves like magnets to the surface of the part and build-up until it is covered. Eventually, the part surface itself becomes charged, at which point oncoming particles are repelled and the coating process stops, yielding a smooth, even film thickness across all surfaces of the finished unit.
Heating of the surface is normally accomplished at PPG Coatings Services with natural-gas-powered ovens. As described earlier, thermoplastic powders typically require the part surface to be heated prior to the application via the fluidized bed technique. Thermoset powders are most often applied via the electrostatic spray technique with the part at room temperature. The part surface and powder coating are then heated simultaneously.
Curing of the coating applies exclusively to thermoset powders, as thermoplastic powders normally are not cured. After the part surface is heated to the desired temperature (360º-380ºF), it is held there for a specified time, normally 20 minutes, while the curing agent develops the desired film properties.
Coatings Types and Applications
Epoxy powder is normally preferred if a tough durable film is required. It should not be used if the coated part is expected to be exposed to direct sunlight for long periods of time, as the coating will form a chalk-like appearance under such conditions.
Polyester powder is widely used for decorative components where good resistance to ultraviolet (UV) rays from sunlight is important. Acrylic powder is specified when decorative requirements are greater and extended UV resistance is critical. Many high-visibility automotive trim and exterior components are coated with polyester and acrylic powder coatings.
A powder coating system with the appropriate supporting equipment, such as the treatment system for process fluids, represents a significant capital and staffing investment. For low-to-moderate production volumes, outsourcing is a cost-effective way to obtain the advantages of powder coating.
When production volumes reach the levels that could justify an in-house system, the decision to outsource for powder coating becomes more complex than a "make-or-buy" evaluation. At that point, it also becomes a “strategic” decision that requires answers to two fundamental questions: “What is our business?” and “Do we want to run a coatings operation?”
Here are a few advantages of outsourcing with PPG Coatings Services:
- Project Analysis: PPG Coatings Services assists with development; then implements and supports the most effective processes to meet and exceed customer goals.
- Building and Equipment: PPG Coatings Services designs, builds and manages coatings' operations for maximum efficiency specific to the customer’s product.
- Coating Application: PPG Coatings Services provides highly trained personnel for total custom coating system management.
- Parts Handling: The customer takes full advantage of PPG Coatings Services’ experience in packaging, logistics, assembly, inventory control, masking and specialized fixturing.
- Long-term Management: PPG Coatings Services’ unique “bundle” of skills and technical expertise allows customers to focus on their core businesses without the worries of operating a coating facility.
PPG Coatings Services offers powder coating services in multiple U.S. states and in other countries. Complementary technologies, such as electrocoating and liquid painting, are available at certain locations as additional coating service options.
Well known for the capabilities in its internal Technology Group, Equipment Division and experienced operating teams, PPG Coatings Services has earned a reputation for providing a total, integrated, cost-effective coating solution.
For more information regarding our locations and services, please call 877-786-9670.