The development of conductive inks, printing processes, and roll-to-roll capabilities for manufacturing of electronics is a fast-growing market. There is an increasing market demand for printable conductive inks for applications in radio frequency identification (RFID) tags for tracking inventory, photovoltaics (PV), sensors, vehicles, smart packaging for anti-theft and anti-tampering purposes, smart cards, printed batteries, electrochemical sensors, flexible displays and lighting, smart food monitoring, wearable sensor networks and touch screens. Silver nanoparticle, silver nanowire, copper nanoparticle, carbon nanotubes and graphene conductive inks are commercially available.
Image 1: Screen‐printed electrodes for disposable devices (Image courtesy DropSens).
Nano inks
Nanomaterial inks are marketed by several companies for printed electronics applications, and can be deposited easily onto a variety of rigid and flexible substrates with standard coating techniques including spray coating and Aerosol Jet printing.
Inkjet printing is also being used to deposit various types of conductive nanomaterials such as gold and silver. Although these metals are excellent conductors, CNTs are potentially cheaper and more versatile as they can behave as both a semiconductor and a conductor.
The conductive ink segment of the printed, flexible and stretchable electronics market was estimated at $2.4 billion in 2015. There is a potentially large opportunity for nanomaterials in these markets, as they are excellent candidates for flexible, high performance, environmentally-friendly, printed devices at reduced cost. Graphene and SWNTs have been identified as viable alternatives.
Graphene conductive inks
Graphene conductive inks (GCI) require no heat treatment and are more conductive than other carbon-based alternatives to silver inks. They provide superior mechanical robustness, flexibility and enhanced interfacial adhesion to improve lifetime and performance of printed electronics, while providing significant cost advantage over silver-based inks currently widely used in printed electronics industry.
GCI can be printed onto flexible substrates such as polyethylene, paper, paperboard and label stock on standard using the roll-to-roll process. Desirable properties include:
- Higher conductivity – as much as 10x higher than typical carbon inks
- Lower cost – compared to widely used silver based inks
- No high-temperature sintering required for current inks
- True flexible applications where bending, folding, handling, dropping, and even crumpling do not disturb the printed circuitry.
- Energy storage batteries printed directly into flexible, plastic substrates.
- Chemical inertness, and mechanical flexibility.
Main target applications for graphene conductive inks include:
- Flexible electronic circuitry.
- Flexible and large-area displays.
- Radio frequency identification tags (RFID) tags and devices.
- Smart labels.
- Portable energy harvesting and storage.
- Smart coatings.
- Printable antennas.
- Printable biomedical and environmental sensor arrays.
- Intelligent packaging.
Printable sensors
The growth in the IoT has created an ever-increasing need for low-power, printed sensors. There is a consistent market need to make sensors smaller, more responsive and cheaper. Main growth markets for sensors are in consumer and mobile electronics. Automotive, healthcare and environmental monitoring markets are also important. The main idea of smart or intelligent structures is to functionalize the structure itself, so that it is able to detect and adapt to variable effects of the environment. For this purpose, sensor-actuator systems are integrated into the structure, mechanical values like stress, strain, acceleration or force are measured and the electrical output signal is fed back to the signal processing unit to control the actuators.
The development of printed strain sensors, which can be integrated in lightweight structures for monitoring purposes is desirable. However current sensors used in these markets have including flexibility, stretchability, sensitivity, and stability for certain applications. Also, the development of cost effective, reliable and functional sensors for electronic skins has been a challenging. Application of such skins include haptic interfaces, robotic manipulation, and physical human-robot interaction. Silver, PEDOT:PSS, CNT/polymer composites and graphene-based conductive inks are key enabling materials for flexible pressure or strain sensors for these applications.
Image 2: Carbon nanotubes flexible gas sensor (Image Technische Universitaet Muenchen).
Printed batteries
The growth in flexible electronics has resulted in increased demand for flexible, stretchable, bendable, rollable and foldable lithium-ion batteries (LIBs) as power sources for application in flexible and wearable devices. Flexible LIBs are generally referred to as LIBs that can operate within the normal elastic range. When the external force is unloaded, it can completely restore its original state without any remaining plastic deformation or bending. Although there remain significant technical and fabrication challenges to overcome, widespread application of applications of flexible LIBs with superior electrochemical and mechanical properties in flexible electronic devices is expected.
Printable antennas
Key to the wider adoption of passive ultrahigh-frequency RFIDS is reducing the cost of the antenna. Manufacturers have printing antennas, but the cost is equivalent to the cost of metal antennas, with reduced performance. Therefore, here is a need to develop advanced materials applications to meet this requirement. Graphene ink has been widely developed used as a conductor in printed antennas.
Image 3: Graphene ink antenna (Image courtesy Vorbeck Materials).
REFERENCES
The Global Market for Conductive Inks to 2027, Published August 2017, Future Markets, Inc. Read more at https://www.futuremarketsinc.com/the-global-market-for-conductive-inks/
