Paint makers go the extra mile

Recent advances in paints and coatings are not only meeting the demands of aviation’s most demanding clients, but are taking care of the environment – and workers’ health

For many business jet owners, their aircraft is their “business card”. It may be the first thing a potential client notices about them, according to RUAG Aerospace, which maintains and refurbishes aircraft at Munich’s Oberpfaffenhofen Airport for OEMs including Bombardier, Gulfstream, Cessna, Dassault Falcon and Embraer.

As well as creating a good first impression, RUAG says today’s paints and coatings also protect and preserve the value of the owner’s asset. Clear topcoats that resist weathering and UV light keep aircraft looking “factory new” for longer.

Julie Voisin, aerospace product manager at US paint manufacturer Sherwin-Williams, says that while all sectors of the industry are looking for longer-lasting paints, the topmost priority for the business jet owner is appearance.

“The aircraft has to represent him; the finish must almost look like glass,” she says. “It’s important to commercial airlines too, but for them, the surface area is much larger and the time constraints tighter. They have to get back into the air as quickly as possible.”

AkzoNobel, the world’s largest paint and coatings company and a major producer of the speciality chemicals they contain, says the decorative finishes that are now possible, including liquid metal effects and eye-catching multi-colour effects that vary according to the angle of observation, give business jet owners the opportunity to strengthen brand identity.

“The GA (general aviation) segment generally requires the highest level of aircraft appearance and a greater level of topcoat quality than other aviation segments,” comments Mark Cancilla, global director, coatings at PPG Aerospace. “While aircraft utilisation rates are not nearly as high as in the commercial segment, and the service life demands of the products not as stringent, the appearance of the topcoat must maintain very high quality levels.”
Topcoats using PPG’s Andaro special-effect pigments bring a new level of brilliance to exterior colour schemes and are now being used in the livery of a major global airline. Formulations are now being developed for other aviation segments, and will provide mica and metallic colour effects, Cancilla says.

‘Match my plane to my shoes’
PPG is leveraging its expertise in the automotive OEM and refinishing businesses to meet the increasingly complex demands of the aviation market, Cancilla says. Vincent van der Laan, global marketing specialist for AkzoNobel Aerospace Coatings, says his company has also adapted technology from its automotive division to develop two-part basecoat/clearcoat systems for aviation.

402nd Maintenance Wing workers apply the PreKote Surface Pretreatment to a C-5 Galaxy.

The demands of high net worth owners can be very exacting, Voisin points out. An aircraft may have to precisely match the colour of a sports car, a motorcycle or even a pair of heels. The technical issue this raises, however, is that in other applications, paints don’t take such a harsh beating from their operating environment and don’t, for example, expand and contract as aircraft do in flight.

Sherwin-Williams is beginning to receive more requests for chrome-look or pearlescent paintwork, but although pigment companies have products available, they are not yet consistently meeting aerospace requirements, she says.

Achieving good adhesion between the coating system and the substrate is critical because of extreme environmental conditions including wind abrasion and the need for the coating to “flex”, Cancilla confirms. To cope with the various substrates found in the industry, PPG and its competitors have developed a range of specific paint removers, selectively strippable systems surface preparation materials and primers.

In the traditional single-stage (or more accurately single-product) process, the paint contains all the resins and other additives needed to make it resistant to UV light and chemicals such as hydraulic fluids and fuel.

If the paint shop is going right back to the bare substrate or shell, it first has to pre-treat the surface, providing corrosion resistance in the case of aluminium or evening out irregularities in the weave of carbon fibre. After priming, a “sacrificial” sanding surface is applied to fill in any unevenness caused by seams or rivets. This is sanded almost completely away.

Only then is the aircraft ready for its topcoat, which in the single-stage system is applied in multiple layers. Each coat can take 10-12 hours to dry, so where additional colours, stripes, logos or special graphic effects are required, a midsized business jet could be out of action for one to two weeks.

Not only do the latest two-stage paints offer improved functionality, they also allow faster turnaround. Sherwin-Williams claims the SKYscapes basecoat/clearcoat system it launched earlier this year saves up to 30% in process time, reducing labour input as well as materials and energy.

The base coat is heavily pigmented and its improved colour hiding technology means fewer coats may be required if a previous livery is being overpainted. It flows out evenly and eliminates the sanding layer stage.

The newer, so-called high-solids paints may sound heavy, but in practice they are applied in such thin layers that overall weight can be reduced. The largest commercial airliners can carry up to four tonnes of paint, and with fuel accounting for 25% of their costs, scheduled airlines – and private jet operators too – are looking to shed weight wherever they can.

Moreover, because the paint layers are faster drying than in the past, a fresh coat can be applied every two hours if necessary, or three coats in a single eight-hour shift. No baking process is needed, which means the paint shop not only saves time, but also significantly cuts its energy bill.

The final step is to fix the basecoat with a high-performance clearcoat containing all the special resins needed to provide UV resistance and durability. Colour fastness is improved, cleaning and buffing is easier, and the repainting interval can be up to 30% longer.

There are some similarities between the processing needs of the commercial aviation and business aviation markets, PPG’s Cancilla points out. Both want to reduce process times, cut the amount of solvents used through the system and remove chromates from primers, for example.

However, resistance to hydraulic fluids such as Skydrol is a much more important requirement in the commercial sector. “Skydrol is very aggressive to paint systems and can strip some coatings if left immersed,” Cancilla says. “By contrast, in business aviation a buffable clearcoat is a ‘must have’ while in the commercial aviation market it is hardly ever asked for.”

Andrew Richardson, global market director at AkzoNobel Aerospace, also points up the differences between the general aviation and commercial markets. “While the GA aircraft needs protecting just like a commercial aircraft, there is a bigger focus on the client’s image and an imperfection-free finish is a must. That means no orange peel, no runs or sags and no blemishes in the finish.

“We have developed an Alumigrip basecoat/clearcoat system that meets the individual demands of the general and business aviation market, rather than trying to take an existing ‘commercial’ basecoat and applying it into this niche market.”

A long time to market
Each OEM has its own specifications and unique demands in addition to industry-wide standards such as AMS 3095, meaning that it can take from three to five years to bring paints from the laboratory to commercial application, Voisin says.

As well as researching better-performing, more durable coatings, manufacturers have been devoting equal effort to developing systems that protect workers and safeguard the environment.
Most suppliers now offer chrome-hazard free primers alongside their regular primers, but although non-chrome is well established in Europe, Voisin says the US has lagged behind.

“Companies want to do the right thing by their employees but also for owners,” she comments. “It’s human nature not to embrace change if you know that what you’re already doing is giving customers a good final product.”

AkzoNobel pioneered chrome-free primers for aircraft exteriors back in the early 1990s with the launch of Aviox. “This was applied over a chrome-free pretreatment by a couple of airlines at the time, with KLM being the front runner,” says Richardson. “KLM painted over 100 aircraft in a totally chrome-free exterior system, and in-life performance showed that the system worked as well as the chromate containing systems.

“When you replace chromate containing primers and pretreatments, you cannot look at the individual products that make up the system and puzzle together a chrome-free solution,” Richardson continues. “The performance of a topcoat is reliant to some degree upon the primer or surfacer underneath, and that primer upon the pretreatment. An airline or business owner cannot hope to get superior results from a topcoat if the wrong type of system is underneath.”

AkzoNobel’s water-based Metaflex SP1050 is a chrome-free pretreatment that can replace Alodine 1200 chromate containing primers as well as chromated washprimers. “Not only do we see superior corrosion performance in a number of systems but Metaflex SP helps with paint system flexibility and helps reduce process time,” Richardson says.

It is often regulation rather than voluntary good practice that forces change. Thus all paint manufacturers have been working since the late 1990s to reduce volatile organic compounds (VOCs) and these formulations rapidly became standard, in part because the law demanded it.

It was more recently that hexavalent chromium came under the health and safety spotlight. Yet despite the technical advances manufacturers have made, Voisin estimates that chrome-based corrosion resistance treatments still account for more than half of the market.

Repair shops have been waiting for proof that chrome-free products can do as good a job, she says. One major OEM has conducted four years of tests but so far has not made the results public.

Likewise there is resistance, especially in smaller facilities, to the high-solids paints. The products are actually beneficial in terms of lower VOCs, and their colour retention and depth of image is at least as good Voisin says. The issue is simple lack of familiarity, and perhaps fears of cost, though she says these are unfounded.
High-solids paints may look more expensive up front, but when the on-cost of protecting workers from traditional paint types – and of responsible waste disposal – is taken account, there is little difference. Paint shops do not have to invest in new application equipment and, importantly in this global market, can apply the products with equal efficiency regardless of variations in temperature or humidity, Voisin claims.

Investment in environmentally friendly coating technology under the motto “going green” has proved cost-effective for RUAG Aerospace.

The chromate-free primers RUAG now uses contain only 7% solvent, saving three to four tonnes of solvent per year. “The new procedure better protects the health of employees as the product no longer contains carcinogenic materials. The adhesion of the primer to the substrate and protection against corrosion can also be improved,” explains Hermann Bauer, head of the company’s paint shop.

Just as important, RUAG has to apply less paint thanks to the improved covering power of its new paint systems, further reducing solvent emissions and the weight of the finished aircraft.
A new design of spray gun produces practically no overspray, reducing the time needed to mask areas that do not require coating. Guns with high-rotation spraying can now be used to apply special graphics.

At one time, RUAG used several tonnes of solvent per year to clean its application systems. A new cleaning procedure, in which an oxygen and solvent mixture is pumped through the devices, increases cleaning performance and reduces the amount of solvent needed.

Better still, greater paint durability has stretched the length of time before recoating is needed by one to two years – meaning less work for RUAG, but lower lifetime cost for aircraft owners and operators.

Less drag, more range
The latest generation of flexible coatings not only improve an aircraft’s “slipperiness”, but can do a little bit of self-repair to help executive aircraft maintain their pristine appearance.
AIRglide developed a product, initially for sports cars, boats and wind turbine blades, that uses nanotechnology to reduce wind resistance and improve performance. Now adapted for the airline sector under the name Aviation Shield, the coating reforms over minor surface damage such as chips caused by stones or hail.
“It’s like a living surface,” according to Mark Butler, sales director for the airlines division at the company marketing the product, Action Aviation.

First trialled by scheduled carrier easyJet in the search for fuel savings, Aviation Shield has now been developed further. Work by CSM Instruments, whose laboratory specialises in nano-testing, showed a reduction in drag of no less than 42%.

Action Aviation claims that commercial airlines can cut their fuel bills by 4% on long-haul flights and 2% on shorter trips, with payback periods of as little as six weeks.

Talking to us at EBACE earlier this year, Butler said business jet owners may be more interested in the potential for stretched range rather than fuel savings. The product represented a “new paradigm” by potentially allowing some aircraft to make transatlantic flights for the first time, he suggested.

The product, certified to AMS1650c, is applied in two stages. The aircraft is pre-treated in what is effectively an exfoliation process. A negatively charged clear coating fills in microscopic pores on the surface and then a second coating, protecting against UV and hence slowing down sun bleaching, is applied on top. A narrowbodied commercial aircraft can be treated overnight.

Action Aviation claims the coating protects against corrosion and reduces build-up of ice or debris on primary areas. The coating is claimed to last for five years, though leading edges may need to be re-treated after three.

Approvals by Airbus and Boeing will help the product establish itself in the business aviation sector, Butler says. The coating has already been applied on a trial basis to a Gulfstream IV-SP.

AGlaze, a sealant offering similar benefits of reduced drag, enhanced UV protection and longer paint life, has been around longer but again could start to penetrate the general aviation market after recent impressive test results.

As AGlaze cures, it bonds to the substrate, creating an ultra-thin, uniform protective layer. In wind tunnel tests carried out at the Aircraft Research Association last May, an aircraft model treated with the product showed an average reduction in profile drag of 1.3% at an airspeed of mach 0.8.

This exceeded results achieved in an in-service trial by low-cost carrier bmibaby, which achieved a 0.8% airframe improvement (as measured by Boeing’s Airplane Monitoring System) over a six-month period after treating a B737 with AGlaze. The product’s European distributor Airbourne Colours, based at Bournemouth Airport on the UK south coast, is a commercial aircraft painting specialist founded in 2010 and exhibited at this year’s Farnborough Airshow. Andrew Tarry, sales and marketing manager, said the company is now targeting operators of business jet fleets.