Nanomaterials: Enabling the move to inkjet printing of flexible circuitry

We’ve all heard the hype about nanotechnology. Buzz terms like ‘revolutionary’, ‘step-change’ and ‘paradigm shift’ have been thrown around by many people (including myself, I hasten to add!) over the last couple of decades but the impact of nanotechnology within materials science has actually been much more gradual. Nanotechnology needs to deliver on more than just buzz words, and to do so means targeting applications in which a reduced particle size provides a fundamental advantage either by means of enhanced performance, reduced cost or preferably both.

Two such applications are Inkjet Printing and Printed Electronics.

The basis of an inkjet ink is a stable dispersion of solid particles of controlled size and shape being jetted through a narrow orifice. These particles do not need to be in the nanometre range but stabilising nanoparticles can often be easier.

The printing of electronic circuitry onto a flexible substrate generally requires thermal processing of the device at reduced temperatures to avoid damaging the less thermally stable substrate (often organic in nature) and therefore the active material (be it a conductor, semiconductor or dielectric) must also be processed within the same thermal window. In this case, a reduction in particle size will result in reduced curing temperatures.

So, surely at the confluence of these two applications nanotechnology should really make a splash and it is a key market area for Promethean Particles. Promethean designs and develops bespoke inorganic nanoparticle dispersions using continuous hydrothermal synthesis (CHS) and we are currently commissioning the world’s largest continuous hydrothermal reactor system capable of producing multiple materials at ton scale.


CHS offers several key advantages over other potential routes to the formation of nanomaterials, especially when focusing on the production of inks. Broadly, production of nanomaterials can be separated into two classes: dry and wet. CHS falls into the category of a wet-based or dispersion-based production route which gives a number of advantages: production of dispersed nanomaterials solves health and safety issues around the handling of fine dry powders. In addition, the continuous production method is cost-effective, easily scalable and allows particulates to be formulated in situ by incorporating dispersants or capping agents during the synthesis, thus promoting particle stability and removing the need for certain downstream processing steps.

Once produced, the dispersed product is maintained in a liquid state and can be harvested into a wide range of dispersion media by solvent exchange, removing the need for expensive or energy intensive redispersing equipment. Crucially for metallic particles, the accelerated oxidation of reactive metals such as Cu and Ni can be reduced (or even eliminated) by maintaining the particles in a liquid environment.

In my presentation at the IMI Europe Inkjet Ink Development Conference I will show the progress Promethean has made towards offering efficient, sustainable routes to small uniform particles predominantly for application as low-T sintering conductive inks using metals like Cu. The reduced particle size provides opportunities in the choice of print method, and inkjet printing of these inks shows great promise, particularly for fine-feature circuitry on flexible substrates. Promethean’s method for controlling the oxidation process, which has hindered the uptake of Cu within the conductive ink market, is a leap forward in promoting the move away from Ag as the incumbent material for conductive inks.

It is hoped that these cost-effective materials will herald the beginning of high-volume, low-cost printable inks which can be applied to a huge variety of applications from RFID, to sensors, to additive manufacturing; and on an ever-increasing range of substrates from plastics, to paper, to textiles.

Surely this is a paradigm shift??!

Pete Gooden, Promethean Particles