Multiple colours and special effects have brought complexity to airliner colour schemes, although there is still a place for the classic, clean livery. Both requirements bring their own challenges to paint manufacturers and MROs alike.
For a couple of decades or so, there was generally little to excite airliner model builders and collectors, with the industry choosing liveries featuring large blocks of solid colour, straightforward logos and simple designs. But times have changed.
Airlines have recognised their aircraft as large, important branding tools and realised the possibilities of one-off special schemes, making today’s airports considerably more colourful than in the recent past.
Jemma Lampkin, global marketing segment manager, Aerospace Coatings, at AkzoNobel, says: “Airlines are using their livery designs to showcase not only their brand, but to promote special events and partnerships, such as the Olympics, the FIFA World Cup and blockbuster movies.
“It’s not uncommon for us to receive designs with as many as 20 different colours, and these colours are often created specifically for the customer. In addition to the variety of colours, we’re also seeing more requests for special effects and metallics. These are relatively more challenging to produce than typical solid colours.”
Andreas Ossenkopf, director and head of aviation at Mankiewicz, adds: “There’s a trend towards more elaborate colour schemes, but also a move towards cleaner liveries. The so-called Eurowhite – white, blue and red – is still a classic.
“Here, we have to distinguish between flag carriers, whose liveries are increasingly simplified, and low-cost carriers, which use bright colours to stand out at the airport. Many airlines also opt for ‘theme planes’, which can be quite colourful. Here, the Mankiewicz BaseCoat/ClearCoat system offers airlines many possibilities, enabling bold colours to shine through in a very long-lasting high gloss finish.”
Like Ossenkopf and Lampkin, Julie Voisin, global marketing manager at Sherwin-Williams Aerospace Coatings, notes that colourful liveries are as popular, as special-effect finishes.
They’ve been available to airlines for many years, but are becoming more prominent than ever. “Etihad, for example, employs a gorgeous gold, while American employs a silver mica on the fuselage. So, micas and special effect coatings are being used over large surfaces and for highlights.”
Special finishes are gaining considerable traction in the executive and VIP aviation market, where cost and the ground time required for extended, highly skilled application processes are less of an issue to operators.
Voisin says the airlines can, to a degree, offset the additional cost of special coatings through economies of scale when larger numbers of aircraft are involved.
Aircraft painting requires considerable skill to do well, regardless of finish or process and Voisin says Sherwin-Williams offers customers extensive support. “We have a technical service group that travels around the globe assisting customers.
“It could be that they want to try a new product, or they’re having an issue, or even that they’re doing a special aircraft and want to ensure it turns out right. We’d rather be involved at the front end of the project, helping with colour and product selection.”
The support extends to defining what type of spray gun ought to be used, the optimal environment for application and training in how to use the product. “I remember one scheme that involved 17 shades of grey.
“Our tech service people were on site and laid panels out along the wall. They practised with the painters before they went and worked on the plane. We’ll use similar techniques on practice panels, to ensure repairs work out properly too,” she continues.
Generally speaking, aerospace coatings are applied as systems, rather than simple paints, designed to achieve optimal effect and recognising that a great deal of the importance of a finish is, in fact, skin deep.
“Coating system design begins with the substrate and location on the aircraft,” Lampkin explains. “Aluminium will remain a key substrate for many years, so corrosion protection is a key performance property. We’ve developed new, eco-friendly solutions that protect exterior aluminium alloys from corrosion and provide a smoother surface that enhances the finish of the final paint scheme.
“Composites are also playing an increasing role in aerospace components, presenting a different set of challenges. They don’t corrode, but they do micro-crack at the surface. Composite primers therefore need to be more flexible, without sacrificing their chemical resistance, resulting in a delicate balancing act.
“The OEMs are manufacturing entire fuselage shells based on traditional thermoset composites and considering more novel thermoplastic composites for future models. The problem is that most traditional aerospace composite primers don’t readily adhere to these new surfaces without extensive pre-treatments and preparation processes.
“Our research & development team is focused on developing a new range of products for this purpose, although we already offer a successful primer, Aerodur Barrier Primer 37045, based on a unique hybrid epoxy-urethane polymer structure.”
“The manufacturing processes for composite components are not yet as fully developed as those for metal parts, which frequently results in surface defects,” Ossenkopf reckons.
“Despite the application of several coats of paint, such irregularities can remain clearly visible. As a consequence, Mankiewicz provides fillers for the various types of surface imperfection and production processes to make surfaces fit for finish. These include ALEXIT RapidFill and SEEVENAX KnifingStopper and, for large irregularities, SEEVENAX SprayFill, for fast-filling spray application.”
Airlines want their aircraft looking good, as shining brand ambassadors, but they also want long-lasting, resilient finishes applied economically in the shortest possible turnaround times.
As a result, Ossenkopf says: “A coating system must perform to perfection, from primer and filler to clearcoat, and from initial application to many years later. We take great care to achieve short drying times, excellent hiding power and stable application parameters to meet the requirements of MROs and their airline customers.”
Sherwin-Williams’ Voisin explains the critical purpose of primer as protection. “The philosophy with airliner painting is to apply as good as possible a finish as quickly as possible.
“So, where a business jet would receive a ‘sanding coat’ on top of the primer, a commercial aircraft does not. Then, when it comes to top coats, we have Jet Glo Express, a single-stage polyurethane that’s applied in a couple of coats and provides all the protection necessary.
“Alternatively, there’s our SKYscapes Basecoat/Clearcoat technology, where the colour Basecoat is put down as quickly as possible and the Clearcoat is applied on top to bring all the protective properties. The choice between the two techniques depends on how many colours are applied and how exotic the design.
“Imagine a scheme with four different coloured ribbons that intersect and cross over one another. For that, Basecoat/Clearcoat would work better, because the multiple colours could be applied quickly and then the whole thing Clearcoated at the end.
“For a basic design, overall white with a couple of simple stripes, (for example, the single-stage technology), might be more efficient. Also, for the metallic or mica effect the Clearcoat is essential. Most important in all this is drying time – 12 to 14 hours for the single-stage system, two to three hours for Clearcoat.”
AkzoNobel’s Lampkin says direct involvement with the airline is critical, especially when a change of livery is planned. The company worked with United on its recent rebrand and was involved early on in the process.
“This allows us to work with the designers to ensure the envisioned colours and designs meet the airline’s appearance objectives and the MRO’s application requirements.” She confirms AkzoNobel’s attention to drying times and notes other finish parameters of key importance.
“Aircraft manufacturers and operators always welcome weight reductions, especially during the design and certification phases, and we contribute to these benefits, perhaps saving dozens or a few hundred pounds overall, although our primary focus is on developing functionality.
“Our new Aerobase and Aerodur basecoat and clearcoat systems, for example, were developed to improve durability and reduce application time. Then we found ways to optimise our colour formulation for optimum brightness and opacity, which can lead to fewer layers and lower film build and weight.”
Weight reduction is also an important focus at Mankiewicz, where Ossenkopf explains: “The lowest possible dry film thicknesses and smoothest possible surfaces, which offer dirt little chance of adhering and keep air resistance as low as possible, are just two aspects of helping reduce weight and increase efficiency. We take care to develop coatings that develop their full property profile and cover completely, even in very thin film thicknesses.”
Resistance is critical
Looking good is about more than quality application and high-tech products. Resistance to the harsh elements that come into contact with an aircraft’s skin in day-to-day operations is also critical, both from aesthetic and airworthiness points of view.
Lampkin notes: “Aerospace coatings are developed to perform against aggressive requirements. These include large temperature fluctuations, UV degradation, and Skydrol and corrosion resistance.
“The industry uses thermoset epoxy and urethane chemistries to provide the resistance properties, always balancing requirements to create systems that adhere to the substrate, but can be ultimately removed on demand.
“The aim is to produce a finish hard enough to resist harsh chemicals, but also sufficiently flexible to endure the rigours of flight. At the same time, it should be low in VOC [volatile organic compounds], but capable of producing a smooth, ‘orange peel’ free film.”
Coatings manufacturers have therefore invested in creating finishes that look good and perform well in service, while keeping in mind the MROs, which need quick, efficient application processes and fast drying times.
But what about when an aircraft needs repainting? Typically a less than environmentally friendly necessity, what is the industry doing to ease the stripping process?
Lampkin explains: “The removal of tough, high-performance polyurethane and epoxy coating layers, down to the substrate, is typically done with chemical paint strippers. It’s a relatively inefficient process that creates quite some chemical waste.
“But we also offer products optimised for use in selectively strippable systems, including Aerodur HS 2121 Primer, which, when used with Aerodur 42240 Sealer as an intermediate coat, enables customers to use relatively mild paint strippers.
“The approach selectively lifts off the top coating layers, eliminating the need to build up the entire paint system, reducing waste and solvent emissions. Our newly Boeing-qualified Aerodur 2111 chrome-free primer is removable with non-acid based paint strippers, while first-generation products required hazardous acid-activated paint removers.”
In addition to its own environmental advances, Voisin says Sherwin-Williams constantly works on processes and products where productivity is the primary driver.
“We want products that are super durable and satisfy our customer’s demands for performance. They need to get the aircraft finished as soon as possible, but it may not get painted again for six or seven years, or until its next C check, so the finish has to last.
“I was with a customer recently and asked them: ‘If your paint could do anything, what would you wish it could do?’ He wanted faster drying times, and we listened carefully to that. Meanwhile, our chemists are working hard to improve the efficiency of our raw materials and we watch technology closely. It’s a balance between listening carefully to what our customers want and bringing new ideas to the table.”