It's not just parts related to the electrical infrastructure of electric vehicles that are now being powder coated. In addition, automakers are considering powder coating for suspension and cooling system components because it is efficient, durable and has minimal environmental impact. While traditional North American automakers have avoided using powder as a body coating (primer and topcoat) since the early 2000s, emerging automakers in Asia are starting to use powder color topcoats. Entry-level automakers have been using ultra-durable polyester topcoats over electrocoat for the past few years.
Powder coating process
The "dry-on-dry" powder coating scheme has been around for many years. The true dry-on-dry powder coating process has encountered difficulties in production scale due to the dispersion of different powder particles (primer and topcoat) during the application process. In recent years, powder manufacturers
have refined this concept into a four-step process that includes:
. Apply a dry powder base (primer).
. Infrared heating gelation.
. Apply a dry powder topcoat.
. Full oven cure.
The added gelation step results in a two-coat system that combines excellent corrosion resistance with excellent UV durability.
Powder in-mold coating (PIMC) technology has been around since the late 1990s for a process called compression molding. A thermosetting powder coating is electrostatically sprayed onto a preheated mold/tool used to make plastic parts. Plastic, usually in sheet form, is placed into the mold, which is then pressed together. When heated, the coating and plastic substrate fuse together to form the finished part. More recently, manufacturers have developed molds that can simulate the look of carbon fiber in a powder coating that is not only aesthetically pleasing but also extremely tough and durable.
Architectural Coatings
Ultra-durable powder coatings are gaining momentum in the market. Fluoropolymer powders have been used on many large skyscraper projects to provide excellent UV resistance. The most notable of these are 55 Hudson Yards in Manhattan, the Stratus Building (9th and Lenora Streets) in Seattle, and PNC Plaza in Pittsburgh. These powder coatings are based on special fluoroethylene vinyl ether resins and are cured with an aliphatic polyurethane crosslinker. The technology exceeds the stringent requirements set forth in AAMA 2605 and Qualicoat Class 3 specifications and can withstand intense UV and environmental exposure for up to a decade or more.
Raw Materials
On the raw materials side, new gloss reduction and matting materials have been developed. Bernhard Resch of Evonik reported on a new spherical amorphous silica that can reduce gloss from 90 GU (gloss units) to well below 40 GU. This unique functional filler, called Spherilex, is inert, has a low specific gravity, and in many cases can improve the impact resistance and flexibility of the coating. Calistus Ezeagu of allnex introduced a new matting resin designed to cure with a β-HAA (hydroxyalkylamide) crosslinker. This polyester material produces an aesthetically pleasing matte finish with a gloss level of 10-15 units and good color and bake stability. The resulting coatings have excellent flexibility and film smoothness.
Smart Powder Coatings
Some of the more interesting developments include powder coatings that respond to environmental stimuli. A Spanish powder manufacturer has developed a photocatalytic powder coating that absorbs harmful nitrous oxide in the environment and converts it into harmless nitrates when exposed to UV light. These guys have also developed a powder coating that repels insects, most notably mosquitoes that carry disease-causing bacteria and viruses. Lab tests have confirmed that this coating technology can reduce the population of Aedes aegypti, a mosquito known to spread dengue, Zika and yellow fever in tropical climates, by 62%.
Heat-Sensitive Substrates
The powder industry has renewed interest in curing technologies for heat-sensitive substrates such as composites, molded plastics, assemblies and thick-gauge parts, natural wood and medium-density fiberboard (MDF). This has led to a renaissance in UV-curable powder technology.
