Intelligent packaging is engineered to sense change in the environment within or external to the contents in a package—or on the package structure itself—and to respond by signaling the change. Among the intelligent packaging technologies that have been proposed, developed, or even introduced in recent years have been time-temperature integrators, maximum temperature indicators, radio frequency identification (RFID), tracking systems, interactive information generators, microbiological spoilage indicators, and even pathogen identifiers. That there is a paucity of commercial food packaging applications to date should hint that the highly publicized intelligent packaging has not yet reached technical maturity.
Some sense of the latent desire for greater intelligence in and information from packaging has been demonstrated in the electronics industry’s recent investments in growing the adolescent discipline from chemical color signalers to microelectronics using printed circuitry, tiny batteries, solar power, or even dipping down into nano-size technologies.
Understanding Printed Electronics
Originally authored by Chris Lo and published on the website www.Packaging-Gateway.com, an excellent overview piece on printed electronics is summarized and paraphrased here to offer food packaging professionals an update on this key platform for intelligent packaging. Printed electronics are an ultra thin electrical circuit surrogate. The electronics are printed on an inert flat or flexible substrate using modified conventional printing technologies such as screen or rotogravure and conductive inks.
As has been alluded to in prior Food_Technology packaging columns, printed electronics have been applied in other disciplines to flexible photo-voltaic solar cells, RFID, and temperature indicators but have hardly scratched the surface within the packaging industry. According to Packaging-Gateway author Lo, printed electronics appear nearly ready to edge into food packaging as the cost of the technology plunges. Further in the future, printed electronics may be a means for food packagers to implement concepts such as illuminated packaging (lights on, everyone), self-heating and/or self-cooling containers using thermoelectric principles, self-contained RFID, and nutritional quality and microbiological safety alerts. And, of course, generated electrical signals may be applied for control of temperature, gas concentration, or even delivery of antioxidants and antimicrobials.
Food Packaging and Printed Electronics
Among the several organizations focused on printed electronics is NovaCentrix (www.novacentrix.com), noted for expertise in nanomaterials for photovoltaics and innovative display technologies.
This company asserts that the intense heat-based processing required to set conductive printing inks so they are effective degrades the conductivity. The additives and presumably solvents that stabilize conductive inks are removed by heat. Printed electronics are usually applied on flexible or semi-rigid substrates such as thermoplastics or paper and paperboard materials which, of course, are sensitive to the high temperatures.
Despite the challenges, NovaCentrix states that its PulseForge processing tools can now render printed electronics a viable food packaging adjunct. Photonic curing delivered by the PulseForge equipment heats the inks only to the required processing temperatures without damaging the substrates.
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By replacing the laydown, strip, and adhere thin film circuitry traditionally used for RFID with copper-based electrically conductive printing inks on high-speed printing lines, the new electronics could reduce RFID costs by a factor of 10, Lo reports.
Developers of printed electronics have been working to reduce the cost of conductive inks. Thanks to its high conductivity, silver has traditionally been used as the basis for functional inks. Particle-free silver ink has a lower processing temperature than standard silver ink. However, cost is a barrier, limiting its applications in food packaging.
Copper is a much less expensive conductive metal than silver, but until recently was not considered feasible for printed electronics because of its rapid oxidization, which often completely destroys the ink’s functionality. Using the photonic curing cited above, NovaCentrix starts with copper oxide ink and reduces it to metallic copper, a well-known conductor.
Other potential alternatives are being researched, including graphene ink (derived from graphite) developed by a research team at Cambridge University in the United Kingdom.
Inks on Flexible Package Materials
Substrates vary in properties that affect the ink conductivity. Inks may become brittle and crack when the substrate flexes. The ink may flake off or not adhere fully to the base.
With the prospect of built-in flashing signal lighting and pictorial optics, video broadcasts, integrated tracking technologies, electrical potential quality sensing, and the many additional innovations that printed electronics have the possibility to provide, food packaging companies should be motivated to quickly educate themselves to an active understanding of the possibilities for the direct application of electronics for intelligent packaging. And what has been enumerated above can only be a hint of the future potential.
Printed Temperature Sensing Tags
Norway’s Thin Film Electronics (Thinfilm) and South Africa’s PST sensors (PST) are jointly developing a printed circuit temperature sensor system. These systems represent an example of how low-cost electronics can be manufactured in high volumes for a fraction of the cost of traditional silicon microelectronics. The printed sensor system is able to monitor primary food packages to ensure that their contents have been maintained at optimal temperature. Thinfilm (www.thinfilm.no) has also announced technology relationships with Sweden’s Acreo (www.acreo.com), which develops printed displays, and Imprint Energy (www.imprintenergy.com) of Berkeley, Calif., which is developing printed zinc-based battery technology to power microelectronics. Thinfilm has established networks to enable fully printed integrated systems and smart tags.
Thinfilm recently demonstrated a working prototype of a roll-to-roll gravure type printed non-volatile memory device addressed with complementary organic circuits, the organic equivalent of CMOS (complementary metal oxide semiconductor) circuitry. Thinfilm Addressable Memory combines the company’s polymer-based memory technology with transistor technology from PARC, a Xerox company, using complementary pairs of n-type and p-type transistors to construct the circuits. The addressable memory can be integrated with other printed components to create fully printed systems for interaction with everyday objects—ovens, refrigerators, and healthcare providers’ records. It’s a key part of the company’s vision of the “Internet of Things,” where virtually any item can communicate with any other.
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Partner PST develops ambient processed printed silicon electronics focusing on physical sensors. PST has a portfolio of prototypes including decorative large area temperature sensors and thermal imaging arrays. PST’s temperature sensors are based around a core technology of a printed silicon NTC (negative temperature coefficient) thermistor, a device whose electrical resistance decreases when it is heated. Being both printable and electronic, the sensors can be fully integrated with Thinfilm’s memory and with complementary organic circuits.
“The combination of our printed addressable memory and a PST temperature sensor creates a new category of integrated system—inexpensive, intelligent, and able to offer information on temperature on a per item basis—something not currently possible due to manufacturing and material cost restrictions,” said Thinfilm’s Jennifer Ernst ([email protected]). “These systems will let food packaging professionals know that perishable food such as meat or eggs has been correctly refrigerated. Ultimately, these devices may even tell consumers how fresh their food is.” Bemis Corp. has linked with Thinfilm to produce an intelligent packaging platform for flexible packaging.
Thinfilm has taken another step toward replacing traditional semiconductor components with fully printable systems. Typical sensors for this market are said to cost between $15 and $25, while the integrated devices developed by Thinfilm and PST will have a price in the range of $0.30 per unit. Not yet economical enough for primary food packaging, printed electronics clearly are headed rapidly downward in price and upward in ability to render food packaging a more comprehensive communications medium.
A pioneer in printed electronics, Thin Film Electronics provides fully printed non-volatile, rewritable memory for applications in toys and games, logistics, sensors, and ID systems.
Key drivers in this research on enabling intelligence in food packaging structures have included the imperative for more information on the contents, increased oversight on the microbiological safety and quality, and the ability to interface with distribution channels, which is so important under the new food safety regulations.
We regard one of the more significant advances to be the potential to convert intelligence signals to drive control mechanisms and thus activate the packaging by enhancing its functionalities. Marketing professionals are already linking on-package information to smartphones and talking to consumers in the store about nutritional values and recipes. Communication between food packages and appliances such as microwave ovens and toaster ovens is beginning. RFID has functioned with distribution packages. And laboratory and pilot electronic developments promise to establish close informational bonds between consumer minds and food packaging. The long-sought systems integration of food, packaging, and delivery has appeared on the horizon with these and other applications of micro-electronics and perhaps even nano-technologies.
Aaron L. Brody, Ph.D., Contributing Editor
President and CEO, Packaging/Brody Inc., Duluth, Ga.,
and Adjunct Professor, University of Georgia