Paint plays an important role in aircraft cabin finishing, as a protective coating, aesthetic solution and even as a mood setter. Now, through the latest technologies, a variety of new, textured and special effects coatings is available, adding colour in an exciting, durable and efficient extension to the cabin designers’ palette.
Modern airliner cabins are all coloured plastics, composites and films – aren’t they? Apparently not. According to JulieVoisin, Sherwin-Williams Aerospace Coatings global product manager, of the total paint quantity employed on each aircraft, 40 per cent is on the outside, 30 per cent on hidden structure and the remainder in the cabin and cockpit.
“There’s typically paint on the overhead bins, the tray tables, around the seats, in the galleys and the lavatories, and in the cockpit. A big advantage of paint over coloured plastics for areas like tray tables and overhead bins is the ease with which it can be touched up.”
Over the past decade, paint manufacturers have added textured finishes to their standard ranges, creating a variety of coatings that are surprisingly useful, not least in their ability to achieve great uniformity of finish. Like regular paints, they are chosen for their colour, but also for their haptic qualities (essentially the way they feel when touched) and their optical performance, since the texture affects the way they reflect light.
Eric Rumeau, CEO at Mapaero, says this utility is achieved while satisfying various demands on material performance. “Fire resistance is most important, where low heat release, low smoke emission, low flammability and minimal release of toxic gases are required.
“At the same time, paint must adhere to all cabin substrates – metal, composite and plastic – drying with high scratch and stain resistance, while applied at a thickness of just 50μm [2 mils or 0.05mm] and providing consistent texture and lustre, and homogeneous colour.”
On the subject of safety,Voisin adds: “Paints have to suit flammability requirements, just like any other cabin component, with testing to ensure burn, smoke and heat release parameters meet regulations. Further to that, people eat on planes and that can produce some pretty difficult stains, so we put our coatings through stain resistance trials as well.
“Every paint that goes into the aircraft also has to be tested for flammability in combination with the substrate it’s applied to. Every manufacturer tests the materials being used and they’re then tested together; paint characteristics might even vary with colour and whether a primer has been used.”
And is there regional variation in regulatory standards? “Airbus and Boeing, as the primary OEMs of large aircraft, set a consistent standard that they both work to and this effectively sets the global market standard.”
Stefan Jacob is sales director aviation at Mankiewicz, which offers a range of textured coatings: “We have a wide variety of textures available, from extremely fine to very rough, as well as from soft, textile haptics to a really course texture, which appears sandblasted. It’s even possible to add metallic pigments to some textured paints, giving even greater freedom of design, making many new effects possible and satisfying the varying demands of use in economy, business and first class.”
At the same time, these coatings have to be exceptionally tough and continue looking good through extended periods of service. “Our ALEXIT SelfTex and textured topcoats are highly durable,” Jacob says. “They have to be. Consider how many times wheeled suitcases are slid into overhead luggage bins every day. Unlike with their own cars, for example, passengers are not particularly careful in how they treat aircraft interior surfaces. Every painted surface therefore has to be scratchproof and robust. Here, textured paint offers an advantage in that small scratches that might be easily visible on a smooth surface are rarely noticeable.”
Exposure to ultra violet may cause exterior paints to fade and although the cabin is less prone to the issue, Jacob notes: “All our ALEXIT-FST cabin coatings are especially light resistant, guarding against the possibility of discolouration or other impairment.”
Sherwin-Williams’ catalogue includes a selection of effect coatings, including JetFlex Elite. “It’s a new product that takes some of the solid colour technology that’s been approved and used at Boeing for many years, and adds ‘pearls’ and effects. It provides options for delivering a different look.
We believe it adds a little more class and accent to premium cabins, perhaps with silvers and golds, or muted blues. Most of the JetFlex Elite colours require only a single-stage application too, where effect paints often require a clear coat on top.
In addition, we have some two-stage whites that appear to change colour as ambient lighting varies.The product might appear golden, changing to blue as light levels increase, for example.
“We’re also bringing out Jet Suede, which has a leathery, suede-like feel. It’s excellent for areas in an airliner cabin, or even in a business jet, where the designer might want to put leather but it’s not the best product. It might be a high-wear area or somewhere that needs regular retouching; Jet Suede can produce that look and feel, easily and regularly touched-up and with less expense.
“For us, these special coatings are about providing a toolbox of options from which designers can choose, providing highlights and cabin textures.” In which case, does Sherwin-Williams offer a complete range of textures and finishes in coordinated, matching shades? “Absolutely. We could supply a solid grey for economy, with the same shade in suede-feel for first class and an accented, ‘pearl’ finish in business class.”
She talks about applying effect, colour and tone to the cabin, but with airlines increasingly looking to colour-changing LED mood lighting to produce ambience, could it be argued that coatings are being reduced to a canvas upon which the computer- controlled lights paint?
“I think colours should complement mood lighting. Choose the wrong colour and you can get a dingy, dark effect as light hits it, when what you really want is a bright, clean effect.
“So yes, I believe colour selection remains critical, but considered within the cabin as an entire concept, ensuring all the components and details work together. Designers need to consider the paint colours alongside the lighting, just as they’d think about the seat fabric compared to the carpet.”
In fact, paint is so important to the finished product that its manufacturers may become involved in the cabin design process during the early stages. “They might come to us talking about a colour in the catalogue,” Voisin confirms, “but wanting to see it perhaps in a range of three shades lighter and three shades darker.
We create that and they might choose one of the resulting colours to then see that as three shades lighter and two shades darker. In that way we customise it for them, helping create something unique.
“The design process may take three or four years to complete and be approved.Then the programme of cabin refurbishment across the fleet might last six or seven years, perhaps even more.”
To ensure consistency of shade throughout, Sherwin-Williams keeps a formula, ‘a combination of colourants’, on file, forever – Voisin says she can easily pull up formulae from right back to the 1970s. A sprayed panel also goes on file, carefully stored to avoid light damage. Finally, solid colours are stored digitally, as a series of spectrophotometer readings.
Remarkably, Voisin says any of the stored formulae could be produced in any of Sherwin-Williams’ current products, in line with modern regulations. On the other hand: “It’s surprising how often we get a call from someone who painted their cabin 20 years ago say, and wants to touch it up. We just go into the records and produce that colour for them again. And we can account for variations in shade over the aircraft’s life using a portable spectrophotometer that we take out into the field.”
Apply with care?
Rumeau says the technology behind creating a textured finish employs different sized particles of specific density within the paint. “Our Di Tex coating, which is especially favoured for cabin ceiling components and cockpit structures, is sprayed just like any other paint, either manually or by automated process.
“Two or three layers of wet paint are applied. Water then evaporates during the drying process, revealing the texture, followed by a polymerisation that creates a robust network in the paint film. As long as the painter reaches the indicated thickness range, the texture will be achieved, but no special skill is required for successful application.”
Aviation coatings, especially when they produce ‘special effects’, have been demanding to apply, requiring a high degree of operator skill. While that’s essentially still true for large external areas, cabin coatings have become somewhat easier to work with.
Mankiewicz’s Jacob uses its ALEXIT SelfTex as an example: “It produces a textured, homogenous surface directly from the spray gun, regardless of the equipment used and operator style. It even makes parts produced by different manufacturers appear as if they came from the same mould. And only a single layer of ALEXIT SelfTex is needed, making application particularly easy and efficient.”
Aircraft cabins contain a variety of materials, from plastics, through various composites to metals, complicating the process of achieving an even finish.
Factor in the various base colours or original finishes these products might have, and any top coat has a potentially tough job consistently covering the substrate below.What’s the tactic for achieving a successful finish?
“Most of our interior products have high coverage and the colour of the substrate has no influence on the final colour shade,” Jacob says. “When a substrate is very smooth, only one layer of paint is applied for reasons of economy.When it is rough, filler and/or primer are used to achieve a smooth base layer, preventing irregularities showing through to the topcoat. In essence this proves the guiding principle in coating application, that perfect finishes start with the first layer.”
Sherwin-Williams’ products are designed so that wherever possible they will cover a variety of substrates. “But if we do need assistance,”Voisin says, “we use a primer to help adhesion and appearance that obviously goes between the substrate and topcoat.”
She notes that considerable skill is still required when paint is applied to large external areas of an aircraft, but that’s less the case for smaller sections in the cabin. “We designed JetFlex Elite to be ‘painter friendly’. It’s simple to mix and apply over the smaller components in the cabin; painters like it because it’s so easy to handle.”
Logic would have it that a textured surface is more likely to trap dirt and attract grimy marks than a smooth, shiny equivalent.Yet Jacob says that thanks to the formulation of Mankiewicz’s coatings they are actually less prone to becoming dirty than some smooth surfaces.
“Cleanability is among the great strengths of our interior paints.We ensure they withstand even the strongest cleaning agents during our test process, so the regular cleaning processes used in aircraft are no problem.”
Describing Mapaero’s Di Tex product, Eric Rumeau says: “We’ve optimised cleanability, testing against tough stains including coffee, mustard, ketchup, ink and lipstick. Di Tex is highly resistant to chemical attack, so it’s easily cleaned, and experience shows it performs exceptionally well in everyday use.”
Rumeau and Voisin were both quick to mention food stains when discussing their respective products’ resilience. How many of us have, unthinkingly, plucked a dropped morsel directly off the tray table and eaten it? Is there a call for antibacterial qualities as well as stain resistance in such areas?
“There’s a trend towards antimicrobial coatings,” Voisin agrees. “But there are many facets to it, bacteria, viruses and so on. It’s difficult to devise something that will attack all those possibilities and still be safe to use on a tray table – for now, it’s where careful cabin cleaning, and products resilient to tough cleaning are really important. In future, I think the market will increasingly call for paint with antimicrobial qualities.”
Beyond, simple repairs, Jacob reckons undamaged cabin paint requires replacement only during the standard cabin refurbishment that comes as part of a D check, roughly every seven years. Rumeau says the existing paint is sanded, or the surface reactivated, before a new finish is applied.
Repainting might also occur as the result of a change of ownership, lessor or branding, however. JulieVoisin explains how Sherwin-Williams satisfies the contradictory requirements of creating coatings that last, with delivering products that are removed with minimal environmental impact.
“Sanding the coating and then reapplying is usually sufficient for a refresh – stripping it down can be a little tricky and isn’t generally necessary. Even though it’s very durable, the paint is very thin, maybe 1 to 1.5 mil, compared to 1 mil of primer and 2 to 3 mil on the outside.”
Advancing technology has cleaned up aircraft painting a lot, although inevitable environmental impacts remain. Mankiewicz offers textured coatings in solvent and water-based variants. “The environmental impact of water-based coatings, which are used globally, is entirely negligible, from application through to removal and disposal,” Jacob notes.
“Water-based paints have proven successful in use for decades.Their latest generation is also extremely fast drying, which can halve the energy used in their application. Moreover, they possess high transfer rates, significantly minimising unwanted overspray.
Rumeau reinforces the reduced environmental impact of water-based paints, reporting VOC levels below 150g/l for Mapaero’s DiTex products. Nonetheless,” Jacob says, “some customers still prefer solvent-based paints.The solvents have a certain amount of impact on the environment, especially during the initial application process.
As these coatings dry, however, the solvents evaporate completely and there are no further negative consequences for the environment. “Using fillers can reduce the quantity of paint required, obviously reducing any environmental impact, since only one layer of paint is often necessary.
This reduces process times, andsaves energy and material. “The continuing challenge for paint manufacturers is to achieve a durable, robust finish that’s pleasing to touch,” Jacob says. “In order to do that successfully, it’s important for us to establish what’s required by working with the customer to select the most suitable product.The fulfilment of fire, smoke and toxicity [FST] requirements also has an important role to play, perhaps especially with critical FST substrates.
“Looking ahead, we see a trend where customers want to select from a toolbox of diverse products, choosing those that precisely fit their design concepts. Custom solutions and designs are increasingly popular, and our textured paints are key components for satisfying this need.” he adds.
“Their reparability has also been optimised, so that should a repair be necessary it’s possible to complete simply, leaving the blemish almost invisible. We have numerous repair solutions for various types of damage.
“These range from simple repairs carried out on board to more advanced fixes; the former includes a single-component bottle and brush touch-up, while we also offer two-component kits.”
“The particles that provide the texture are encapsulated in the polymer matrix of the paint,” Rumeau explains, “and therefore resist scratches and stress. The paint’s durability is very good as a consequence, but we nonetheless offer a touch-up kit. It exactly reproduces the shade and texture when sprayed over a damaged area.”
Minor damage to textured coatings is relatively easy to repair, especially compared to fixing films or other covering materials, which typically require a degree of dismantling before a fix is applied.
And by comparison with coloured plastics, paint offers another major advantage: “Optical performance is key – airlines want passengers to experience a unique shade when they enter the cabin and presenting a patchwork of hues is out of the question.
“It’s very difficult to get consistent colour with plastics, because the pigment mixing is done at higher viscosity and high temperature and dispersion is not particularly efficient. Colour dispersion and reproducibility is easily achieved with paints, because their liquid and dispersion is completed at ambient temperature.”
Editor’s Note: The post was originally published in July 2018.