Aerospace coatings: a survey of aircraft manufacturers and coatings suppliers.

Responding to increasing regulatory and price pressures, as well as growing expectations for "greener" products and services, the airline industry (commercial and military) has challenged aircraft manufacturers to provide airplanes protected with environmentally friendly, high performing, durable coatings. Aircraft manufacturers then look to coatings suppliers for products that enable them to satisfy the airline companies' needs.

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Coatings Tech surveyed representatives from various aerospace companies and coatings suppliers to ascertain their views of the current state of coatings performance in the aerospace market. Aircraft manufacturers were asked what they like about the currently available coatings and any improvements they could recommend. Several coatings suppliers' representatives were given the opportunity to respond to these comments. To ensure the most open and complete responses, all participants were assured that their comments would remain anonymous. A summary of the results of the survey and related comments are presented here.

POSITIVE DEVELOPMENTS

When aircraft manufacturers were asked what they consider to be the top positive features of the coatings already in use, all recognized the ability of today's paints and coatings to maintain low VOC content while offering reasonable longevity, UV stability, and cleanability. It was also pointed out that the use of exempt solvents has increased pot life, reduced dry times, and improved rheology characteristics, making these compliant and "greener" coatings more user friendly. One respondent also noted that current primers have good Skydrol resistance. Although the aircraft companies surveyed like the performance of chromated primers for good corrosion protection, they acknowledged the need for chrome-free replacements.

In response, coatings producers stressed that new chrome and lead hazard-free primers that have been tested to aerospace standards for all commercial, military, and general aviation aircraft now meet three key industry requirements: they apply faster, provide uncompromised protection of aircraft substrate, and comply with OSHA regulations for lead and chromate exposure.

MAKING IMPROVEMENTS

When asked to elaborate on desired performance improvements, aircraft manufacturers focused on durability challenges such as color/gloss retention, adhesion in high erosion areas, and crack resistance over composites. Other coating properties that they would like to see improved include impermeability to water and other solvents for galvanic couple resistance and the hydroscopic nature of fillers used in surface coatings.

Coatings suppliers recognize that aerospace coatings must withstand a great deal of punishment and have to meet a wide range of specifications. Products are designed to meet the requirements of specific programs such as SAE International's Aerospace Material Specification 3095 (AMS 3095) for Airline Exterior Systems. In doing so, said one coatings supplier, the coatings address performance concerns and provide excellent coverage and protection for most types of aircraft.

With regard to durability, one coating producer explained, "We put a lot of effort in developing products that meet requirements--for instance, lifetime corrosion protection and Skydrol resistance--and in delivering high solid and waterborne coatings that replace the conventional technology and reduce VOC and throughput time."

Another coatings supplier acknowledged that the issues raised by the aircraft companies are a reality, but also pointed out that performance requirements have increased rapidly. Coatings producers are working to develop new "breakthrough" innovations and next-generation formulations that address these issues. "We are constantly striving to accelerate the development of advances in coatings technology that will lead to improved performance and application processes."

STREAMLINING PROCEDURES

Outside of specific performance properties of the applied coatings, the aircraft manufacturers that responded to the survey would also like to see improvements in curing, application, and removal processes.

With regards to curing, one respondent noted that some coatings are too dependent on the curing mechanism (infrared cure, ambient cure). Another survey participant conveyed concerns about the sensitivity of some coatings to the humidity and temperature of the environment in which they are cured. Another would like to see cure times significantly reduced so that the application process can be more efficient and productive. This reduction in application time must be achieved, though, without sacrificing durability and in-service performance, acknowledged the respondent.

Other areas of the application process that were highlighted for potential improvement include the consistency of rheological properties to provide less orange peel and better overall appearance, the ability of coatings to better tolerate inferior surface preparation, the tendency of high solids coatings to have greatly reduced pot life times with increased temperatures, and problems with the sprayability of low-VOC coatings through HVLP and electrostatic equipment.

MEETING THE CHALLENGE

The coatings suppliers responded with a number of product examples that are proving successful in the aerospace market. New fluorinated resins, according to one respondent, enhance color and gloss retention in topcoats. Plus, these coatings can be accelerated at room-temperature cure using accelerators and are found to also be easier to clean and maintain over the maintenance life of an aircraft.

High-performance exterior coating systems, such as multi-component polyester urethanes, have set the standard for easy and effective application, according to another coatings company representative. "These coatings offer excellent flow and leveling properties, as well as faster dry and cure times. This improves processing flow and helps to quickly return an aircraft to service."

UV-curable coatings are also currently being explored as an alternative to speed up dry-to-fly times to minutes instead of days. The main obstacle, according to one coatings supplier, is capital expenditures on equipment that can position a UV light source on all areas of an aircraft at one time for complete cure.

High solids polyurethane coatings do pose some issues that coatings manufacturers are trying to address, stated one respondent. They react with moisture and heat and, as a result, locations with variable high heat and humidity differentiations will have difficulty maintaining consistent cure times, which can affect appearance. Low solids polyurethanes tend to work better due to lower applied film build; however, VOC content tends to become a problem without the use of exempt solvents. However, some exempt solvents are extremely flammable and therefore are not used due to fire codes.

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Appearance can be controlled, though, through operator use of the proper tips, caps, and gun settings to achieve better atomization. "Far too often the operator sacrifices appearance for the option of completing a job in a shorter amount of time," noted one coatings producer respondent.

With regard to preparation of the substrate, coatings producers emphasize that proper preparation is necessary to ensure proper adhesion. "At this time, there is no miracle paint that wipes the substrate clean, removes the contaminant, and then adheres itself to the substrate," said a coatings supplier representative.

INTO THE FUTURE

Aircraft companies were also asked as part of the survey to look forward into the future and describe the advances in coatings technology they would like to see from coatings suppliers. Most mentioned the addition of advanced functional capabilities and characteristics including drag reduction, anti-icing, low solar load, lightweight, superhydrophobic, and self-cleaning. "Suppliers need to ask the question: 'How can the coating system help to reduce weight and improve maintainability of the aircraft?'," offered one aircraft company respondent.

Other aircraft company representatives would like to see ultra-durable coatings with, ultimately, a 30-year service life that exhibit excellent color and gloss retention and adhesion to rivets and in high erosion areas. A good self-priming topcoat that has ultraviolet resistance equal or better than the current topcoats would be beneficial and a savings in time and weight, said one responder. "Cure on demand" capabilities via methods that are feasible for paint hangar facilities (both OEM and refinish) and rework/repair scenarios are also desirable.

As mentioned earlier, the development of non-chrome corrosion inhibitor packages that equal or exceed the performance of current hexavalent chrome corrosion inhibitor packages was cited by all aircraft manufacturers as an immediate need. Finally, topcoats (available in any color) that are resistant to temperature increase due to solar heat absorption are desirable.

The coatings suppliers indicated that most of the recommended advances in coatings technologies mentioned by the aircraft companies are, in fact, being investigated. Some products are already in the pipeline. For example, heat- and solar-reflective coatings are currently being evaluated by different customers for a few specific colors. Self-priming topcoats are being re-evaluated as new and better surface preparation techniques evolve. And work continues on non-hexavalent chrome corrosion inhibitors to improve their performance beyond that of hexavalent chrome. "These efforts are close to coming to fruition in the next few years," said one supplier respondent.

Another coatings supplier added: "Coatings technologies continue to advance in terms of ease of application, lower emissions, and meeting regulatory compliance--while still improving durability, performance, and providing outstanding color. We will continue to move ahead with coatings technologies that provide our customers with faster turnaround through the prime and color coating process, as well as providing continually advanced, highly durable aerospace products that withstand the extreme rigors common to this industry."

WORKING TOGETHER

In addition to asking aircraft manufacturers about coatings performance, CoaitngsTech also sought their opinion on the relationships they have with their coatings suppliers. Respondents indicated that they would benefit from more collaboration earlier in the development process. "We would like to see the formation of user/supplier technology partnerships to more effectively develop and implement new technologies," stated one aircraft manufacturer.

They would also like coating manufacturers to be more knowledgeable about how their products are used at the OEM level.

Specifically relating to the development process, one respondent recommended that coatings suppliers invest more in the development and utilization of relevant test methods (corrosion, adhesion, appearance, ability to clean, etc.). "Coating manufacturers could solicit input from OEMs on their coating needs early in the development stages, then continue to work with the OEMs throughout the development and testing process to refine the material and make improvements, which will help ensure that coatings that are developed meet the customer's needs," one participant believes.

In response, the coatings producers feel that they do work closely with their customers in the aerospace industry. "Coatings manufacturers go to great lengths to incorporate OEM input and needs in the coatings R&D process. We prefer to partner whenever possible with aircraft manufacturers to assure that coatings utilized in their re-paints are just as durable and performance-driven as those applied when the airplane was new--and in many cases, even better," asserted one respondent.

Another respondent stated that his coatings company works closely with OEM and military services to understand the needs and performance criteria the coatings need to fulfill. "In some of our projects, we work solely for a customer and, to a certain degree, integrate some of their key knowledge experts into our development process."

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"Aerospace coatings manufacturers pride themselves on providing responsive, ongoing contact with their customer base by offering such services as on-site training sessions and technical support and interactive, online tools, such as color visualizers, to help OEMs and designers do their jobs better. Widespread global distribution networks dramatically speed up custom orders, often resulting in delivery and application within only a few days from the initial order," added another coatings supplier representative.

Even given this belief that strong relationships have been developed between coatings suppliers and aircraft manufacturers, there is recognition that further collaboration can happen. According to one coating producer, it is only a matter of time before aircraft companies and coatings manufacturers will join forces in all aspects of development, from idea generation to screening of best candidate solutions to development and delivery. "We've got the feeling that we are now in the phase from sharing knowledge and experience to full partnership within a multi-functional team," commented a coatings supplier representative.

OTHER SURVEY INSIGHTS

Asked if there were any other key issues not previously discussed, aircraft manufacturers highlighted a few additional topics of interest. One respondent would like to see coatings be more compatible regardless of the supplier, so that primers from one coatings producer could be used with topcoats from another.

With regard to communications, one aircraft company noted that coatings producers should use OEMs' material and process engineering groups as the points of contact for introducing new coatings and coatings processes prior to contacting production areas.

Most importantly, aerospace coatings users wanted to emphasize that there is a tremendous opportunity to reduce cost associated with commercial airplane refinishing. Currently, airplanes are taken out of "revenue service" for several weeks every four to six years to be repainted. This cost to the airline industry could be reduced with higher durability finishes and more efficient refinishing processes, according to survey participants.

A number of coatings manufacturers responded to these comments with their own request for the aircraft industry. Currently every OEM has its own specifications, many of which require development of customized products due to slightly different requirements. Coatings producers see an advantage in OEM companies joining forces to define one specification for a certain application (fuel tank coatings, for example). The coatings suppliers do recognize that this type of system is unlikely to be developed in the near future, though.

In the meantime, coatings companies continue to focus on the development of new, advanced coatings technologies, such as basecoat/clearcoat systems. According to one respondent, shifting to this technology from traditional coatings can eliminate entire portions of the painting process, trimming turnaround time by upwards of 30%. This, in turn, would directly and significantly increase profit as airplanes can be back in business almost a third of the time faster.

"These new systems can also afford the opportunity to optimize coatings for weight, performance, repair, and color retention, which translates to more cost effective management of the aircraft life cycle for a fleet operator," offered a coatings supplier representative.

The survey responses and corresponding comments show that while aircraft manufacturers and coatings suppliers may not always be in sync, they are both constantly working to meet the needs of their customers, from the coatings laboratory to the friendly skies.

Survey Participants

AkzoNobel Aerospace Coatings

Boeing

Cessna

Deft

Lockheed Martin 

The Sherwin-Williams Company

by Cynthia Challener JCT COATINGSTECH Contributing Writer