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In the past ten years, research and development in powder coating materials has resulted in new formulations that have paved the way for powder in directions previously only accessible to liquid coatings. Following an overview of the types of materials used in powder coatings is a summary of the versatility of today’s powder coatings.
Types Of Powder Coatings
There are two types of powder coatings - thermoplastic and thermosetting. A thermoplastic powder coating is one that melts and flows when heat is applied, but continues to have the same chemical composition once it cools and solidifies. Thermoplastic powders exhibit excellent chemical resistance, toughness, and flexibility. They are applied mainly by the fluidized bed application technique, in which heated parts are dipped into a vat where the powders are fluidized by air, and are used in many thick film applications.
Thermosetting powder coatings are based on lower molecular weight solid resins, and melt when exposed to heat. After they flow into a uniform thin layer, however, they chemically crosslink within themselves or with other reactive components to form a reaction product of much higher molecular weight. These newly formed materials are heat stable and, unlike the thermoplastic products after curing, will not soften back to the liquid phase when heated. Thermosetting powders are derived from three generic types of resins: epoxy, polyester and acrylic. From these resin types, several coating systems are derived. Resins used in thermosetting powders can be ground into fine particles necessary for spray application and a thin film finish. Most of the technological advancements in recent years have been with thermosetting powders.
- Virtually Any Color or Gloss
Color variety is almost limitless these days, with many coating suppliers offering a pallet of off-the-shelf colors as well as custom color match services to better meet the needs of small-volume powder users.
There are also tints which can add highlight color to a substrate or base coat, such as a brass look over polished aluminum.
A range from flat to high gloss is generally available. Smooth, high gloss coatings can offer high distinctness of image creating an illusion of depth or wet looks. Matte finishes can hide surface defects or imperfections such as spot-welds, nicks and scratches on a variety of substrates.
Hammertones or veins give antique or distressed looks created by a black base with metallic pigments of gold, silver or copper contrasting against the black. This weathered look is popular in the furniture and display industries that demand a broad range of multi-color looks, including granite, confetti, rusty and weathered appearances.
Clear powders are often used as an external protective layer on many brass products such as door knobs, hinges, railings, lamps and plumbing fixtures. There are also powders available that can substitute for chrome and brass plating in certain applications, even matching the high gloss of chrome. Clearcoat primers are being used on select models of several automakers. And BMW and Volvo are now using powder clearcoats over automotive exterior basecoats, a technology being tested in a historic collaboration of Ford, General Motors and Daimler-Chrysler at a facility in Wixom, Michigan.
Powder coated finishes can now offer an icy or fluorescent appearance, or the lustrous look of a pearl that may appear to change color depending on the angle of observation. Bicycles, wheel rims, garden tools, light fixtures and some glass products benefit from this look.
Photoluminescent powder coatings are able to absorb the ultraviolet, fluorescent or incandescent light and gradually re-emit the light. These are often available in blue, yellow and green and are used for road signs, hazard warnings, and markings on trucks, buses and police cars.
Metallic coatings, using particles of aluminum, mica, copper or brass, add sparkling highlights that can reproduce the appearance of the base metal and add sparkle to the look of the product. Metallic bonding can physically bond metal flakes to the basecoat powder. A variety of metallic finishes have been formulated for indoor and outdoor furniture, exercise equipment, lawn and garden tools and other products, that can resemble the look of gold, chrome or brass.
Textured coatings are often used to hide substrate irregularities that may show with a smooth finish, provide a non-slip surface or hide fingerprints, while giving a distinctive feel to a product. Appearances vary from the look of fine sandpaper, a pebbly texture or a rougher look resembling alligator skin.
- Advanced Durability
Recent research and testing has developed specially formulated polyester powders that provide even greater weatherability than achievable in previous years, and showing greater success in long-term Florida exposure testing. New TGIC-based powders are used on outdoor stadium seating and other exterior applications that were previously susceptible to degradation from ultraviolet rays. Light poles, lawn furniture, shopping carts and shelving often benefit from powder with polytetrafluoroethylene (Teflon®) additives for increased resistance to abrasion.
- Electroconductive and Electrodissipative
Makers of electronic components sometimes use electroconductive and electrodissipative powder coatings, which provide electrostatic discharge protection of the components, critical during the manufacture, testing and transport of electronic goods. The most common colors for these special powders are black and charcoal, but lighter colors are also available.
- Heat-sensitive Substrates
In recent years, ongoing research and development has been devoted to formulating powders that can cure at lower temperatures, below 212 F, without compromising durability or quality. These powders can be used on temperature-sensitive materials, as well as on massive parts that require enormous amounts of energy with other curing systems. More wood materials, such as particle board and fiberboard, can now benefit from a powder coated finish. This technology has helped to penetrate markets for office furniture, kitchen cabinets and ready-to-assemble furniture for homeowners.
In addition to successfully penetrating the medium density fiberboard market, powder has proven to be an effective finishing choice for other heat-sensitive substrates, such as plastic parts made of nylon and polycarbonate. In addition, assembled or partially assembled products such as appliances, electric motors, automotive radiators, shock absorbers and foam core doors, and other products that may have plastics, laminations, electrical wires or rubber seals, can now also receive a powder coated finish. In addition, heat-sensitive alloys such as magnesium can now be powder coated. Powder coating is also used to color or frost glass products such as bottles or light bulbs.
- Hygienic Powder Coatings
Antibacterial and antimicrobial powders recently developed can help prevent the spread of bacteria and germs on products in homes, hospitals, restaurants, and food processing plants.
- High-Temperature Resistant Powders
Silicone-based powder coatings are often used on products that are subjected to prolonged periods of high heat, up to 1,000 F, and hold their color, gloss, and adhesion. Some of these products include gas and charcoal grills, fireplace inserts, engine exhaust components and lighting fixtures.
- Thin-Film Powders
Powder manufacturers are developing more powders for use in thin-film applications that may range from 0.8-1.2 mils. These powders offer more with less - better powder penetration into recesses, more film thickness control and more effective first-pass transfer efficiency, with darker colors most effective in hiding the substrate underneath.
- UV-Curable Powders
Specially formulated powders can cure by ultraviolet radiation in a matter of seconds, which is one way to cure products with heat sensitive-substrates or components. Many wood products have enough moisture content to provide sufficient conductivity, and electrostatic attraction can be increased by pretreating and pre-heating the wood to promote adhesion.
Other specially formulated powders can be cured in a matter of seconds through near-infrared technology, due to the extremely high heat-up rate. These powders can even work on some heat sensitive materials, because the irradiated energy is almost entirely absorbed by the powder coating layer.
Just as powder coatings can now be used in applications once thought impossible just a few years ago, continued advancements in powder coating formulation will ensure greater powder penetration in markets and on substrates in the near future that arecurrently thought to be unattainable.