Gabriel Alarnes Varela is Key Account Manager Aviation Coatings at Mankiewicz Ibérica. He is Analytical Chemist with a degree on electrochemistry and inmunoanalysis at the University of Oviedo. He has many press releases on technical magazines like Electroanalysis or Electrochimica Acta. He has been working into the coating industry for more than twenty years where he has created advanced coatings for the industrial and military markets. He has also experience on coating testing and ISO 17025 standards.

The aviation industry is a fascinating world where all the different engineering branches join their forces to make true the ancestral human being’s dream of flying. All those efforts gave out this industry many amazing technological developments over the last years.

Every time we compile such innovative items it suddenly comes to our mind the engineering job behind the powerful engines who make a heavy structure flying. Perhaps the avionics or electronics. But let’s be honest. Who think about paints? Maybe some of you might be wondered about the huge amount of paint that an aircraft wears but nothing else. And that’s a fact. An aircraft is coated with a huge amount of paint. Actually, most of the structural parts are painted but there are many reasons behind. You would get surprised if I tell you that the decorative function is the minor one.

This is the core fact that I want to highlight in this article. For the sake of the highest level of safety and durability of the aircraft the coatings are designed to fulfil very restrictive specifications where chemical, physical and even biological properties are required. It is not a minor work. We should keep us aware of the fact that the paint is the skin of this marvellous machine named aircraft.

Looking into details and starting from the “guts” of the aircraft, the revolution of the composite chemistry brought the aviation industry enormous advantages. Due to their strength and lightweight we can fly ultra long ranges with two engine flagships, like the Boeing 787 or Airbus A350. However those revolutionary substrates show a different casuistry when we compare them to the well-known metal surfaces. Therefore the protective coatings must be prepared for the new scenario. The irregularities and shapes on substrates require a full portfolio of “surface correctors” like flexible and physical-chemical resistant fillers, putties and primers. For instance, flexible parts like the engine fan cowls struggle against such severe stress forces that the conventional paint can’t resist and therefore the coating gets collapsed. The special chemistry of new polymers gives out enough elasticity to the paint to overcome such forces and provide a long lasting protective coating on top of the engine cowls.

I would also like to highlight that the latest developments on chemistry made possible to achieve an important target: the birth of the waterbased coatings into the aviation. My company, as a market pioneer, created the water based structural paints for metal and composite parts. Those materials fulfil the same specifications than the solvent borne products with the enormous environmental benefit of the emission decrease of tons of solvents to the atmosphere. Today, the structure of the Airbus family is painted with water. That fact was meant as unreachable ten years ago. Today is a standard.

It might be a paradox if I say that most of the R&D resources are focused on the metallic substrates, which contradicts my previous assert that composite are the future of the industry. There is an urgent reason behind: the elimination of chromates as corrosion inhibitor because of their carcinogen hazard.

Chromates are the best corrosion protectors for aluminium parts, but its hazard makes a priority to remove them from the manufacturing processes. The aircraft industry has already implemented aluminium anodising pretreatments like the Tartaric Sulphuric process (TSA) who get rid of the chromic acid. However, the aluminium protective coatings still use chromates on their recipes. Despite of the fact that the coating manufacturers have already developed chrome free alternatives, the drawback is to fulfil the very strict corrosion requirements that the aircraft specifications require. We should bear in mind that the corrosion is an issue on the aircraft life cycle.

The new era will be chrome free and the paint industry will be soon prepared for such a huge milestone. Regarding the chrome free approach, the exterior painting of the aircraft is a good example. It’s already possible to paint an aircraft’s exterior without wash primer or alodine by means of the sol-gel technology. This sophisticated adhesion and passivation system makes possible to protect the aluminium against corrosion without any inhibitor inside.

his new chromate free sol-gel has also been implemented into the most sophisticated exterior painting system: The Basecoat/Clearcoat. We have to give especial mention to this technology. There is a tremendous gap before and after this scheme has been implemented in the market. In fact, I am so glad to represent the company who made this new era a reality.

The use of a Basecoat who is able to give the full hiding of colours in one single layer, together with the savings on drying times and the revolutionary application of a transparent layer of clearcoat to the whole fuselage meant a huge milestone on weight reduction and process times, durability and aerodynamics (reduction staircase effect). The airlines can’t wait using such a glossy and long lasting system.

Today, the Basecoat/Clearcoat technology is a market standard who beats the older schemes like high solids coatings and let the industry go further on robotics.

But this is not the end on achieving new milestones. Many challenges are still waiting for solutions. For instance, aerodynamics and turbulent flow reduction. We developed functional coatings who simulate the efficient aerodynamic behaviour just providing a functional “shark skin” to the aircraft. The idea is to reduce the turbulent flow and thus the fuel consumption. This effect is achieved by means of a coating who replicates the turbulence reducing riblets that allow sharks to swim at high speed. The stamped riblet structure is covered with a UV curing clearcoat. The application of UV light to the polymerisation of the clearcoat, provides enough energy to accelerate the kinetics in such a way that the varnish is dried in minutes.

The UV clearcoat technology has also been used on ink-jet processes. This technology absolutely fits on the customisation of difficult liveries. The direct printer works as a traditional model, using an inkjet head with nozzles like your printer at home but obviously with huge dimensions to reach a complete aircraft structure. Therefore complex designs are plotted and printed on vertical stabilisers. Afterwards, the ink image is sealed with the UV curing clearcoat.

The use of this technology let the airlines use revolutionary complex designs and the manufacturers go forward on aircraft exterior livery process automatisation with tremendous environmental and safety benefits.
Our acknowledgment to Air Europa and especially Pedro Macias Dominguez, Deputy Chief Maintenance and Engineer Officer at Air Europa, and Alvedro’s staff for giving us the opportunity to take some true aircraft pictures at A Coruña airport.

Learn more:

Shark skin coatings:
https://www.mro-network.com/engineering-design/shark-skinned

Basecoat/Clearcoat:
Smart Painting Process Airbus

Mankiewicz scheme

Inkjet coatings
https://www.airbus.com/newsroom/news/en/2014/09/think-ink-airbus-revolutionises-how-an-airline-s-livery-is-applied-to-jetliners.html

Exterior coatings, shark skin, customer’s experience
http://www.mankiewicz.com/cms/upload/epaper/clearsky/#10