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SWeNT’s CNT Inks Bring Scalability, Ease of Handling to PE Applications  

By David Savastano

There are a number of promising conductive technologies for printed electronics (PE). Typically, conductive metals and silicon-based inks have been most commonly utilized, but other approaches, notably carbon-based inks, have strong advantages as well.

In particular, carbon nanotubes (CNT) offer numerous advantages to PE manufacturers and designers. Single-wall carbon nanotubes consist of a hollow cylinder of carbon ~ 1nm in diameter, up to 1,000 times as long as it is wide. This structure has remarkable optical and electronic properties, excellent strength and flexibility, and high thermal and chemical stability. In addition, CNTs allow developers to provide a very specific functionality for a surface, and can be transparent.

However, there have also been drawbacks to CNT technology. It is difficult to produce CNTs at a competitive cost, and there are ease of handling and safety issues, particularly when utilizing CNT powders.

That is where SouthWest NanoTechnologies Inc. (SWeNT) comes in. A 2001 spin-out of research conducted by Professor Daniel Resasco at the University of Oklahoma, who also serves as SWeNT’s chief scientific officer, SWeNT produces carbon nanotubes using its patented CoMoCAT® catalytic method in fluidized bed reactors. This results in selective synthesis of single-wall carbon nanotubes.

“At the time, single-walled carbon nanotubes were not scalable,” said David Arthur, SWeNT’s CEO. “Professor Resasco developed the CoMoCAT process, which allows single-wall CNTs to be processed in a scalable way, and much to our delight, also allows for significantly better quality control. Now we can produce high- quality single-wall CNTs in commercial quantities at an affordable price.”

Still, improving handling and safety were key issues coming into 2009, but the development of SWeNT’s new CNT Ink has virtually eliminated these issues.

SWeNT partnered with Chasm Technologies, Inc. (Chasm) to launch CNT Inks, based on V2V™ Ink Technology developed by Chasm. These new CNT Inks allow manufacturers to use high-volume printing processes such as screen, flexo and gravure; an inkjet version is in development. Since drying is done at 100°C or less, a wide variety of temperature sensitive substrates can be used, such as polyester, polycarbonate and even paper.

“The SWeNT-Chasm combination creates a lot of synergy, and our CNT Inks have received extremely positive market reaction,” Arthur said. “They are a lot easier and safer to use. These inks are viscous, so they can be printed easily using conventional equipment. Also, the CNTs are encapsulated by the ink vehicle, which addresses concerns about possibly inhaling fine CNT powders. Lastly, our CNT Ink solution forms a very nice film, that when heated the vehicle is evaporated, leaving only the pure CNT layer, strongly affixed to the substrate.”

Potential applications for CNT Ink include photovoltaics and lighting. “We have targeted solar, LED lighting, touch screens and printed batteries,” Arthur said. “We have successfully demonstrated screen printing, gravure and flexo, as well as rod and slot-die for coatings.

“Many manufacturers prefer to print CNTs in specific patterns,” Arthur added. “In addition to tailoring the CNT properties for specific applications, we can now tailor CNT Ink properties for a customer’s preferred printing method.”

While single-wall CNT offer key benefits, multi-wall CNT also have applications, particularly in thermoplastic polymers. SWeNT developed its “Specialty” Multi-Wall (SMW) CNT for applications that require better electrical and mechanical performance than conventional multi-wall CNT, without the cost or dispersion difficulties associated with single-wall CNT. SMW has fewer walls and smaller diameter than traditional multi-wall CNT, thus using less carbon.

SWeNT’s technologies have earned notice. In December, in conjunction with Brewer Science, Inc., a leading producer of CNT inks for electronics applications, SWeNT received a $6.5 million award under National Institute of Standards and Technology’s (NIST) Technology Innovation Program (TIP). The grant will support R&D programs that focus upon methodologies to attain the cost-effective production of high-purity, high-quality metallic and semiconducting carbon nanotube inks.

“NIST has chosen SWeNT nanotubes to be the standard reference material for carbon nanotubes,” Arthur said.

The company is enjoying growth, opening an 18,000 square foot state-of-the-art manufacturing facility in Norman, OK, in September 2008. All in all, SWeNT’s outlook is excellent.

“The opportunities are enormous,” Arthur said. “CNTs will capture its share of the conductive ink market, particularly where customers want multi-functionality. There is much you can do with CNTs that you can’t accomplish with traditional conductive inks. We intend to form additional alliance partnerships to ensure that CNT Inks are available to the market.”