Something Special

Conductive inks are aiding the advancement of smart label converting.

CONDUCTIVE INKS ARE hitting the radio frequency identification (RFID) marketplace and everyone from printers to chip manufacturers are taking notice. They have to. Conductive inks offer many benefits, but first and foremost is cost. A finished RFID tag still costs upwards of $0.30, which—when millions upon millions are needed to meet the demands of large retailers—is a lofty price for consumer product companies to pay.

Much of the cost is due to the silicon microchip, as well as the conversion/assembly process. Traditional copper antennas make up one of the relatively expensive parts at $0.3 to $0.5 per antenna. However, antennas printed with silver-based conductive ink cost just .3 to .7 of a cent—quite a savings where every penny pinched counts, said Jamie Neilson, product manager, Information Mediary Corp./Xink Labs Ltd.

Conductive inks can be printed in-line on standard printing presses and a variety of substrates, making them ideal additions to the smart label converting process. Their immediate impact on the advancement of RFID is apparent.

"One immediate impact on converting is that the inlay/laminating process is greatly simplified," said Graham Battersby, president, Precisia LLC. "Instead of having to laminate a separate solid layer of metal into a tag structure, the antenna can be printed directly onto one side of the web. In the future, there may be opportunities for integrating the printing and converting steps even further. We've seen that different consumer products (such as liquids or those with metals in their packaging) may need different antenna designs to produce optimal RFID performance, so it's conceivable that, as more printers become familiar with conductive inks, they may be able to print the appropriate antenna directly onto the packaging material," he added.

Progress in RFID has been going on since its inception in the 1940s, but has advanced in leaps and bounds since Wal-Mart and the U.S. Department of Defense set out mandates for their suppliers a few years ago. As conductive inks are further commercialized and used more and more, and their reliability and worth is further spelled out in terms of high read rates, they will dominate the market, Neilson said.

"Five years from now, I think printed antennas will be 80 to 85 percent of the UHF (ultra-high frequency) RFID tags and labels (which are the most versatile and useful of the smart labels)," Neilson said.

Printing details

While conductive inks can be printed in-line on the presses printers already have on the shop floor, they are still a different kind of product that requires a slightly different process, Neilson said.

"There are different criteria for judging 'acceptable' printing when it comes to conductive inks," Battersby said.

• Resistance: For one thing, printers probably won't need a densitometer to measure the thickness of the ink being laid to make antennas. They will, however, need an ohmmeter to measure the electrical resistance, or the resistance of electrical flow, through the printed antennas, Battersby said.

There needs to be an acceptable level of resistance for the finished RFID tags and labels to work. While the goal is 100 percent, Neilson said, "expect 85 percent of the performance and read range that you get with copper antennas."

• Material handling: Another important point for gravure and flexo printers to keep in mind is the material handling and planning, since silver-based conductive inks tend to be significantly more expensive than traditional graphics inks, Battersby said.

Also, selecting the appropriate anilox is important to keep ink waste at a mininum. "It's pretty expensive ink so you have to use an anilox that will get enough ink to ensure conductive activity, but not so much as to waste the ink," Neilson said.

• Optimized processes: There's a learning curve with conductive inks while printers find the optimal speed, materials, and processes for printing these materials.

Different conductive inks require specific thicknesses, usually between 2 and 5 microns, for successful RFID operation. This also means the inks have different drying requirements.

"Conductive inks tend to require thicker layers and more drying than graphics inks, so printers may need to adjust their expectations of optimal press parameters," Battersby said.

In addition, some conductive inks can be used to print antennas at speeds up to 300 fpm, while other conductive inks require a slower run speed. Already, however, materials and process improvements have been achieving positive results: decreased drying times and increased press speeds, Neilson said.

They've come a long way since the days when conductive inks were only screen printed. Battersby said, "Polymer thick film (PTF) inks, which have been available for screen printing for decades, were the first example of a dispersion of conductive metal particles in a polymer vehicle. Much work is being done these days to adapt this type of material (and other, newer materials) to higher-speed print processes like flexo and gravure."

by Kate Sharon

Associate Editor