CARC Powder Coatings: An Update

Powder has taken some giant steps forward recently as it strives to be a legitimate contender in the chemical agent resistant coating (CARC) ring. While powder primers have been used for years in CARC systems, only recently has powder stepped up to challenge liquid paints in the more demanding role of CARC top coats. -Paul Mills

Today, CARC powder coatings have been approved as top coats; the military has written new specifications for powder and is investing millions of dollars in powder coating research. Powder suppliers are optimistic that the latest orders for new tactical vehicles due out later this year may specifically call for powder coating technology.

These accomplishments along with the impressive track record of powder primers over the last decade have led many to reconsider the role of powder in military coatings and to think about how other pieces of the coating process, such as chemical pretreatment, can be adapted for a growing role of powder coatings.

Asked about the share of powder in CARC coatings, John Mort, director of sales for aerospace and defense coatings at Hentzen Coatings in Milwaukee, says, “It’s small. If I said 5 percent that would be a good estimate.” He explains that’s not because of any shortcoming of powder coatings, but rather to a system that changes slowly. “If you look at how this market works, it’s really specification driven. All of the engineering drawings to this point have been liquid based. The legacy systems are buried in paperwork that says liquid, liquid, liquid. Since powder has come out so recently, it hasn’t yet had a chance to shine,” Mort says.

But Mort also sees changes coming for powder. “There was so much capacity on the liquid side that prices dropped and there was no reason to pursue powder because it didn’t make dollar sense,” he says. “But the next big contract coming out is for the joint light tactical vehicle (JLTV). The JLTV may be the first chance for powder to really make an impression and create movement in the market. A decision on that project is due as early as December, and I think you will see powder make an impact at that point.”

Experts say that CARC research began when a Russian tank, captured in Egypt in the early 1970s was dismantled and analyzed by U.S. military scientists. Their analysis revealed that the Russians had developed a coating system to provide them with the ability to decontaminate a vehicle if it was attacked by chemical weapons.

Primary Objective: Warfighter Survival

The overarching goal of CARC coatings is to ensure the survival of the American Warfighter. They do this by providing military assets with greater reliability through enhanced corrosion protection and by improving battle readiness by allowing military hardware to be returned to service as quickly as possible in the event of a chemical attack. To accomplish these goals, CARC top coats must satisfy some demanding and somewhat technically opposing needs.

First, CARC powder coatings must provide the proper appearance. This is no trivial color-matching task when some color standards require dead matte finishes below 1.0 on the gloss meter. These colors must also withstand fading in the harsh environment of desert sand and sun. To qualify, these matte finishes must not change color appreciably after extreme exposure conditions. To test these coatings, the most sophisticated accelerated weathering such as EMMAQUA® (Equatorial Mount with Mirrors for Acceleration with Water) is used. Not only must these camouflage colors match standards in a way that meets the eye, but also CARC coatings are formulated to have a distinctive infrared (IR) signature that comes from specific pigments. This characteristic IR signature allows soldiers to identify between friendly forces and foes through the paints spectral properties.

The second broad requirement for CARC coatings is that the coating must be able to withstand attack by chemical and biological agents, be decontaminated, and then returned to service intact. This requires that coating suppliers submit samples to the military for live agent testing against some of the most dangerous chemicals around. To many chemists, the demand for dead matte colors and resistance to chemical agents are somewhat at odds with each other because many of the usual techniques to flatten the gloss of coatings make it more difficult to achieve the other required properties.

This is particularly true for powder coatings. “Many of the additives a powder chemist might ordinarily choose to lower the gloss of a coating to the degree required for CARC also make the powder more likely to absorb live agents,” explains Kevin Biller, president of the Powder Coating Research Group and technical editor of this magazine. “So the powder formulators have had to develop a new set of tricks to achieve the appearance standard while providing a coating that doesn’t absorb chemical agents. That is one reason why the goal of a powder top coat remained elusive for quite some time,” he says.

Buoyed by encouraging technical results and the efforts of some of the industry’s leading coating suppliers, in 2012 the military announced that it would develop a powder CARC topcoat to meet Type III of MILPRF-32348. The Type III was the major step from primers to top coats for powder. The following spring, in what has been termed “a dramatic game changer,” the U.S. Army Research Laboratory (ARL) in Aberdeen, Md., issued the first approval of a CARC powder top coat to Hentzen Coatings. “It took us seven years to get it right. It was a tough combination to achieve,” says Mort. “We have a 40-year history with CARC coatings, so when we approached the new specification we had a database of information, experience and background from the liquid side that definitely helped on the powder side. Instead of starting from scratch, to some extent we felt we were already on the 5-yard line based on knowledge we had already developed.”

To stimulate the development of CARC powder coating technology, the military has also committed to funding extensive R&D in powder coatings. Through the Strategic Environmental Research and Development Program, or SERDP, the Department of Defense (DoD), Department of Energy (DoE), and the U.S. Environmental Protection Agency (EPA) joined together to fund the development of powder coatings for military use by private companies. In 2012, Sherwin-Williams was selected to lead a $1.4 million research and development project to develop an environmentally preferable CARC powder topcoat. Then, in January 2013, in a second round of funding, PPG Industries received a $1.5 million SERDP award to develop a CARC powder top coat.

“The strong part about the SERDP program is that we had partners who had expertise in all the different areas,” says Dr. Beth Ann Pearson, global products manager, Metal and Plastics, for Sherwin-Williams Product Finishes. Her team uses the latest technology, such as electron microscopy and confocal Raman spectroscopy, to understand the design of CARC powders at the molecular level. “The shapes of the molecules for different chemical agents are very different. Therefore, we think about the porosity of the coating and ask ‘what is not going to allow those agents to migrate through the surface of the coating?’ In the past, what really made a coating chemical resistant wasn’t necessarily always well understood—specifically in powder coatings. We have been successful in understanding the intricacies of the polymer network required for decontamination; as a result, we currently have two products listed on the qualified products database (QPD),” says Pearson.

Secondary Objective:
Lower VOHAPs

Although the primary objective of CARC coatings is the survival of our armed forces, there are other forces behind the military’s interest in powder coating development as well. The U.S. EPA wants the military to switch to coatings that are free of volatile organic hazardous air pollutants (VOHAPs), volatile organic compounds (VOCs), and inorganic hazardous air pollutants (HAPs). According to John Escarsega, a leader of the ARL at Aberdeen, “There are many advantages to allowing powder coating to be a part of the program. Environmental is a big reason, but there are also some reduced costs…It’s a good step forward.”

An important justification for federal funding of CARC powder development is the potential reduction of VOCs that can be reduced by using powder coatings instead of liquid paint. The DoD and its industrial base currently emit upwards of an estimated 5.2 million pounds (2,600 tons) of organic solvents per year from CARC topcoat application. According to Escarsega, the use of solventless powder topcoats in high production environments such as depots and OEMs has the potential to eliminate hundreds—if not thousands—of tons of VOCs, HAPs, and other organic solvent emissions per year.

Another driving force is money. “The cost of corrosion is prohibitive,” says Pearson. The DoD spends more than $20 billion dollars a year on corrosion- related damage. “CARC powder is really showing remarkable weatherability because we can create a thicker film with powder coatings. If you talk about the primer and top coat, we’ve got an excellent system to offer for protection,” she says.

“Mil for mil, powder has very good weathering and has seems have a huge advantage over liquid coatings in terms of durability and corrosion resistance,” says Mort. “Where liquid paint has been compared to throwing snowballs at a wall, powder is designed flow out to produce a uniform coating in the form of a continuous film.” He also says that while the current use of powder is low, the places that allow powder to be used have really taken off.

“But the top coat was always the Holy Grail and that was cracked in 2013,” Mort continues. He says the biggest advance is not the technology, but the writing of the specification and the inclusion of powder into new and upcoming contracts. There is a list of approved suppliers on the approved Qualified Products List (QPL), but whether a coating is written into the specification is another story. “Now the specifications are being written so we are capable of actually using those products is the biggest change that’s coming.” Despite the breakthroughs, Hentzen’s Mort concedes that powder cannot rest on its laurels. His own company is already developing a zero-VOC water reducible top coat as well as isocyanate-free CARC liquid coatings that will challenge the latest powder technology.

Sherwin-Williams’ Pearson says that the scientific approach to powder development is critical to the future because CARC coating development is always a moving target. “This approach is really advancing the knowledge needed to deal with the new color spaces that are coming and the chemical agent testing that will be developing. What has been an art in the past is now a science,” she says.

Examining Other Aspects

The progress in CARC powder coatings has prompted the DoD to examine other aspects of the coating process as well. For example, while zinc phosphate has been qualified for pretreatment, it is not the ideal process for powder coating of ferrous substrates. The ARL has undertaken a comprehensive study of alternative pretreatment chemistries more suitable for powder coating systems.

According to Tom Braswell, a senior systems engineer for the Army Research Laboratory (ARL), good progress is being made on this front as well. “We have a couple of nonzinc phosphate products on the QPL right now that work great with powder and five or six more in the loop,” He says. Braswell’s team has been innovative in trying to spur the development of new materials while upholding stringent performance standards. Because of the sunset issues with chrome, Braswell says the team rewrote TT-C-490— the chemical conversion coatings and pretreatments for metallic substrates specification—to qualify other materials as long as they could meet the standards, even if they took a different approach. “We didn’t want to wait around,” he says, “and it has worked really well. By rewriting the spec to allow substitutes for the legacy products called out on drawings as long as they work, we get calls from companies that want us to test their products that haven’t seen in the past.”

Braswell points to work on lower- temperature powder coatings as a frontier for powder in military applications. “There are a lot of opportunities if the powder can cure at temperatures 75 to 100 degrees lower,” says Braswell. Low-temperature powder coatings might not only extend the use of powder to more kinds of assets, but combined with the spray-in-place pretreatments could make powder touch up more attractive, he says.

Pearson also points to the potential for other technologies to shape the future of CARC powder coatings. For example, in 2012, researchers from Rice University and MIT developed a coating with a layer-cake structure made of layers just a few nanometers thick but strong enough to stop a speeding bullet from penetrating the coating. “In the military world, if you have a gas tank and the enemy force shoots it, in the past it would explode. With a self-sealing coating the bullet gets caught in the coating so the bullet never makes it all the way though. That’s an example of smart coating technology that has translated into the military world on the liquid side,” she says.

Technology transfer between military and civilian applications has also flowed in the other direction. Just as innovations from NASA’s space program have spun off everyday inventions such as ear thermometers, freezedried food and cordless drills, the work on CARC military coatings is creating technology that may find uses in other industries. “We are taking the dead matte color technology we developed for military communications equipment and applying it to automotive trim, motorcycles and cosmetic bottles. Designers look at dead matte finishes as sort of the cutting edge of style,” Biller concludes.

Paul Mills is a marketing and business development consultant to industry chemistry and equipment suppliers. He has been a writer for the powder coating industry since 1994. Paul can be reached at 440-570-5228 or via email at pmillsoh@aol.com.