New Process Tech Could Aid Auto Sector’s Move to Powder Paints

LONDON – Until recently, the automotive sector relied more heavily on liquid coatings and resins than other industries.

A major stumbling block in moving to more environmentally friendly and efficient powder coatings was the type of conveyor belts required to move large, heavy auto parts, which can become clogged with powder that can stick to the tracks.

But a breakthrough in the manufacturing process – a floor chain conveyor capable of moving heavy parts and more suitable for use with powder spray application – may clear the way for more widespread adoption in the auto industry for non-Class A finishes.

“Powder offers benefits such as it adheres well, is resistant to wear and could improve the occupational health of automotive workers,” a spokesman for Netherlands-based paint manufacturer DSM says. “Powder offers environmental perks; for example, overspray can be easily recovered and reused up to 95%.”

Developed by a European Union-funded research project called “Powder Protected Cardan Chain in Industrial Floor Conveyors” (Protecc), scientists have redesigned the chain track, including electrical loading of the track and application of a non-metallic outer skin to inhibit powder-paint adherence to the track.

“Applying high voltage to the housing of the track gave impressive results,” says Malte Bethke, a research consortium member for Bremer Kettenmontage of Germany, which installs industrial conveyor chains and oversaw initial development of the Protecc system. “The integrated air knifes (that use compressed air to help keep the conveyor clean) have shown promising results.”

However, development of this track has been slowed in both commercial and technological terms, and designs have not been finalized. It is unclear when the project can resume. Developers are awaiting decisions on further funding applications pending before the European Commission and are seeking investment from commercial interests.

But even without that, technical breakthroughs continue to push the auto sector's move from conventional paint to powder sprays, says Enno Kok, global product manager for in-mold coatings at Netherlands-based coatings giant AkzoNobel.

“We have made some really big steps in terms of smoothness of the layers,” he says. “The specific particle size distribution gives the smoother finish and helps to overcome problems with penetration. Conventionally, if the particles are too fine, they will not charge.”

AkzoNobel also has developed a “low-bake” powder that reduces problems associated with powder spraying thermally sensitive components such as hydraulic parts.

“They are filled with oil, and if you cure it with temperatures of 180º C (356º F) the oil will leak out. The low-bake method can cure at 130º C to -135º C (266º F to -211º F) and also allows us to overcome these problems. There are other applications where the same technology offers benefits with energy consumption,” he says.

Kok says the benefits of powder sprays are clear.

“The environment benefits as powder sprays contain no VOCs (volatile organic compounds), so there are no emissions of solvents. The possibility to reclaim matter is big – you never achieve 100% transfer efficiency, so there is always overspray. With liquid, that overspray is lost, so the yield with powder is higher.”

Interpon, the powder-coatings brand of AkzoNobel, manufactures powder coatings for several applications, from body work and trim to aluminum wheels and in-mold lightweight components. It has developed a powder-based in-mold coating that addresses the issue of heavy finished products by incorporating the powder spray in the manufacture of individual parts. Coatings are sprayed into the hot mold prior to pressing and molding.

Properties include greater chemical resistance to xylene, toluene, gasoline and motor oil; superior adhesion, chip and abrasion resistance properties; and significant thermal shock and humidity resistance capabilities, Interpon says..

DSM, meanwhile, says powder sprays enable parts exposed to corrosion, such as the chassis and suspension of auto and motorbike frames, to be treated with a powder-coating formulation created with resins. These include powder-coating resins for hard-wearing components on trucks, such as the chassis and bumper bars.

“The automotive industry is increasingly switching to our innovative powder-coating resins in line with legislative and consumer trends that call for durable, economical, attractive and eco-friendly coatings,” a DSM spokesman says.

Applications include exterior body intermediate coats (the primer surfacer) for trim parts, door handles and for finishing under-hood components. “By using clear powder coatings, manufacturers have a great alternative to solvent-borne clearcoats for applications like coating alloy wheels," he adds.

However, Kok advises powder sprays still have room for improvement.

“Powder sprays are still a very young technology," he says. Manufacturers, for example, often coat car wheel casings with a primer, a liquid basecoat and a powder topcoat. “This is because the brilliance of the metallic powder is still not exactly the same as the spray.”