The sky’s the limit: PPG on aerospace coatings

PPCJ spoke to Sam Millikin, PPG Global Vice President, Aerospace, about the company’s recent US$17M aerospace application support centre in France and the current and future trends affecting this industry

Q. Why was Toulouse, France chosen as the location for PPG’s most recent  aerospace application support centre?
A. Toulouse has become one of the predominant aerospace industry locations in the world. It has a large aerospace manufacturing presence, including Airbus’ headquarters and a complete supply chain. PPG locates aerospace application support centres (ASC) near major customers to provide them with quick, convenient, best-in-class service. The close proximity to customers also enables us to fine-tune our products to ensure we are meeting their needs and exceeding their expectations.

Q. What is the overall geographic split for aerospace manufacturing – is Europe the main hotspot, or is Asia, or is it fairly evenly split around the world?

A. PPG prides itself on having a large global aerospace footprint, with more than 30 plants, research facilities and application support centres worldwide. ASC Toulouse is our 17th application support centre globally and our second in France. We are located near our customers, all around the globe.

Q. During the COVID pandemic, the vast majority of planes were grounded and that had repercussions on the aerospace coatings industry. Are there still any ‘hangover’ effects from the pandemic, or is everything back to normal now?

A. For the most part, the aerospace coatings industry has recovered, and things are getting back to normal. While there are still some supply chain issues and costs are higher, we saw our volumes return to pre-pandemic levels in 2023.

Q. What are the main challenges when creating an aerospace coating?

A. Understanding the area of end-use for any new product under development is critical to ensure that the coating will perform, as not every chemistry/technology may be suited for use in all areas of an aircraft. As a coatings developer and manufacturer, PPG works closely together with the OEMs to assess the requirements for performance within their specifications. With the requirements and end use in mind, we are then able to tailor the coating technology to meet the need of our customers.

With the ever-changing regulatory landscape, this has become a challenge from a formulation standpoint as some of the traditionally used raw materials (such as solvents, additives and corrosion inhibitors) cannot or will not be used now or in the near future. It can be daunting to find alternative materials that are compliant with regulations while also providing the same or improved performance.

How the coatings are applied in OEM production or aftermarket environments is also critical. The coatings need to be applied in various application conditions such as temperature, humidity and air flow, all of which can range widely from facility to facility (for example, hot and humid to cold and low-humidity environments). All these variations may impact how fast or slow the coatings may respond and can influence the application of subsequent layers, directly impacting aspects from a customer perspective such as throughput and production rates, to appearance (gloss or orange peel) and performance, just to name a few.

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Q. Adhering to regulations and legislation is commonly cited as a challenge in the coatings industry. How does this topic affect your work in aerospace coatings?

A. PPG continuously monitors environmental agencies and regulations for substances that could be put on a candidate list for non-use in coatings in the future. For example, we are working to eliminate hexavalent chrome and nonyl phenol ethoxylates to meet these regulatory mandates. Furthermore, PPG’s sustainability committee establishes guidelines and goals for substance elimination in our products to further our leadership in environmental stewardship.

Q. Can you tell us about any new areas of R&D that PPG’s aerospace division is working on?

A. The aerospace industry is going through a chrome-free conversion as hexavalent chrome-based corrosion inhibitors are eliminated from structural and exterior primers. PPG continues to develop innovative coatings that offer exceptional corrosion protection and are safe for humans and the environment. We now have chrome-free primers that cover all applications on the airframe, including exterior, structural, assembly and fuel tank primers.

Different from spray-applied coatings, electrocoat, or electrodeposition coating, can be applied in a continuous process with nearly 100% coating transfer efficiency. Electrocoat is a proven high-speed, high-performance corrosion protection technology for the automotive industry. PPG first developed automotive electrocoat in the 1970s and has been a leader in electrocoat materials, coatings processes, and services.

Leveraging PPG’s know-how in electrocoat chemistry while addressing aerospace’s unique needs, we developed the first aerospace electrocoat product, Aerocron, several years ago. Aerocron is a game-changer in aerospace primers with outstanding sustainability benefits including absence of hexavalent chrome, very low VOC, and an automated coating process. Aerocron is now being adopted by multiple aerospace OEM customers.

Q. What services will the PPG centre provide?

A. ASC Toulouse enhances our ability to provide unparalleled responsiveness and customer support, leading to faster qualification of our aerospace products and higher participation in new projects, earlier in the development cycle. Capabilities at the ASC include a development and qualification laboratory for aerospace materials, a colour blending area for coatings, and a spray booth for hands-on training. It will also house filling lines for touch-up kits, a transparencies inspection cell, customised packaging capabilities for third-party products, chemical management resources and a customer service centre.

Q. What are the main priorities for your aerospace customers at the moment? What are your customers most concerned with, when it comes to coatings?

A. The two main priorities for our customers are currently supply chain resilience and product sustainability. The market is having a strong recovery following the COVID pandemic, but one of the current limitations lies with the global supply chain.

Another point of focus is around product and process sustainability. Current and proposed  regulations in European having a big impact on the future use of chemicals. Our aerospace business leverages the full power of PPG’s numerous researchers and scientists who stay at the forefront of regulatory requirements and innovations.

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Q. When it comes to sustainability, how does PPG support its customers with this issue and is this more or less of a focus than performance, for aerospace customers? 

A. Safety and performance are the most important aspects of our business. PPG strives to offer more sustainable products into the marketplace. We have worked hard to advance our technologies to meet our sustainability goals and those of our customers.

We have qualified chrome-free primers to replace chromated primers in both the commercial, aftermarket and military markets. For example, PPG Aerocron electrocoat primer is a waterborne, chrome-free technology that is applied electrically in a bath instead of using traditional spray application methods. It has a transfer efficiency of >95%, compared to spray application of ~50%, and is also lighter weight.

In addition, each of our 17 ASCs serve our customers on a regional level and are strategically located near aerospace hubs, which saves on time and fuel costs for delivery. As mentioned previously, the ASCs play a key role in supporting both large, commercial OEMs and aftermarket maintenance of aircraft by providing sealants, coatings, application equipment and repackaging of sealants and coatings. We help reduce waste by ensuring that these products are repackaged for right-size application.

Furthermore, our solar heat management coatings technology is based on infrared-transparent stainers that allow solar heat to pass through topcoat pigments to a white primer coat, which reflects the heat away from the aircraft. This reduces the cabin temperature and saves on energy due to less need to air condition the plane.

Q. And finally, are there any emerging trends in the industry that you think will become a main focus in the future?

A. Electric propulsion is seen as one of the most promising approaches to reduce fossil fuel consumption and the carbon footprint of the aviation industry. Tremendous advancement in electric propulsion has been achieved in recent years. Fully electric urban air mobility vehicles have been successfully demonstrated by many companies. These vehicles are typically powered by lithium-ion batteries and are capable of efficient short distance travels.

Although Li-ion batteries are currently the most efficient battery that can be mass produced, a thermal runaway event of Li-ion batteries is a critical risk for electric aircraft. Multiple materials innovations need to be applied to ensure the safety of these aircraft, such as battery fire protection, thermal interface and insulation materials. An effective recycling process is also needed to enable recovery of the essential metals in the batteries. Steady progress is being made in these areas.

However, medium and long-distance travels are still out of reach for electric aircraft, because of the low energy density, or energy per unit weight, of current batteries. Present state-of-the-art Li-ion batteries have lower than one fiftieth the energy density of jet fuel. Despite a higher energy conversion efficiency of electric motors as compared to combustion engines, drastic improvements in battery energy density are necessary before long-range electric-powered travels can be realised. Concentrated research investments and efforts must be made to develop a novel battery chemistry with higher energy density, low costs, and ease of manufacturing.

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