Introduction:
Powder coatings provide a beautiful, durable, almost porcelain-like finish, while being environmentally safe. They can be applied over many different metallic substrates at film thicknesses selected to meet most requirements.
Powders are formulated in a full range of chemical compounds tailored to fulfill specific and varied coating requirements. They can be formulated to maximize chemical resistance, abrasion, flexibility, or UV resistance.
These coatings are made from polymers that are solid at room temperature. These polymers are then compounded with pigments, curing agents, and other additives in a heated extruder, and then ground into a fine powder.
To create the coating, these powders are loaded into a hopper, from which they are sprayed from a special gun with a high voltage source attached to it. In this way, the particles receive a static charge that causes them to be attracted to all portions of the surface to be coated. With the powder clinging to its surfaces by static charge, the part is then immediately routed into a curing oven at elevated temperature (350˚ to 400˚F) where the re-flow and crosslinking of the powder occurs.
Epoxy Powders:
These were the first powder coatings developed and were based on the now familiar Bis-A/Epichlorohydrin condensates. They were furnished with terminal epoxy groups for thermally-induced curing.
These coatings are generally selected when chemical and solvent resistance combined with toughness, flexibility and wear resistance are the desirable attributes of the end coating. They are not the best choice where regular exposure to sunlight or UV is expected.
Polyester Powders:
Polyester powders came next in the development timeline of powder coatings. They should be considered the real workhorses of the powder coatings industry
The most common form of polyester powder is technically Tri-Glycidyl Iso-Cyanurate. Those in the industry simply call it “TGIC.” It provides a durable attractive finish ideal for exterior use due to its weather resistance, UV absorber content and an easily-achieved glossy, high quality finish.
Acrylic Powders:
Historically, TGIC polyesters have dominated the niche for highly weather resistant powder coatings with acrylics playing a minor role. With the increasing acceptance of acrylics in powder form combined with the widespread acceptance of acrylics in liquid paints, the issue of which is preferable often is asked. Considerable differences in the performance of the two systems exist.
The acrylic coating provides better gloss, clarity, color stability and solvent resistance. The acrylic also cures at lower temperatures than typical TGICs.
In contrast, the TGIC polyester coatings have superior flexibility, impact resistance and shelf stability. In clears, the acrylic has higher flow and better smoothness. In opaque systems however, the TGIC usually shows better coating smoothness due to superior pigment wetting capability. In both Xenon Arc WeatherOmeter and in South Florida exposures, the acrylic shows significantly better gloss retention than the TGIC.
TGIC polyester and acrylic powder coatings can provide high quality, exterior durable finishes. Each type has its own unique advantages and challenges.
Polyurethane Powders:
Smooth, cost effective, UV resistant
Nylon Powders:
Extreme wear surfaces, maximum flexibility. High dielectric properties, clean room approved, outstanding tensile strength.
Xylan Coatings:
Xylan is a proprietary product by the Whitford Chemical company for use as a self-lubricating, wear resistant coating. It has nonstick/release properties, often used in material handling or in conditions of corrosive chemical exposure.
Xylan’s major attraction is that it is extremely thin thus minimizing dimensional effects. It can be applied directly on fastener threads without adversely affecting thread fit and function. For this reason, Xylan coatings are popular on metallic fasteners that must be exposed to corrosive chemicals.
Halar Powders:
Halar is a tradename of DuPont’s (now produced and marketed by Solvay Solexis )for a fluoropolymer coating called ECTFE (ethylene chlorotrifluoroethylene). It combines extreme chemical resistance with high wear resistance. Think of it as a totally inert, high tech version of Plastisol. Its properties make it popular for use in mixers and agitators exposed to abrasive contents that must remain completely pure.
High-Temperature Coatings:
On request, special high-temperature powder coatings can be provided. These coatings have become popular among hot rodders and high performance enthusiasts for their exhaust systems where temperature resistance up to 1,200˚F can easily be provided.
Special Finishes:
In addition to the smooth, high-gloss finishes, many special finishes are available. They include wrinkle finish, hammertone, and flat or semi-gloss.
