Home' FLEXO Magazine : May 2016 Contents Silver and gold are certainly the common conductors that have been
studied, but the problem is they cost a lot of money. Copper is com-
mon as well and has a price advantage over silver and gold, but it can
corrode or oxidize.
The conductive ink market is projected to be worth $3.36 billion by
2018, according to a report from IDTechEx. There is a big market
demand, yet there is not enough variety in ink formulations and case
studies to make the production more cost effective. Further, $735
million will be based on nano silver and nano copper—less than one-
third of this money is focused on current technology. There is a huge
amount of room for brand new ink formulations to seize the market
and become profitable.
Nickel (Ni) is a lower cost metallic element with high conductivity
and is also appropriate to use in ink formulation. It has high resis-
tance to oxidation and corrosion. It can withstand both high and low
temperatures. It has magnetic properties, good for proximity sensors,
micro transformers and inductive charging. It is typically used in mul-
tilayer ceramic capacitors, magnetic devices, printed energy storage
devices (as a current collector layer to enhance the use of stored pow-
er and to reduce overall energy consumption) and as electrodes and
conductive interconnects for supercapacitors and flexible electronic
Large pigment particles require higher temperatures for drying/sinter-
ing and they are prone to settle over time. They also limit the ability to
obtain fine features. In contrast, nano particles have smaller diameters
and higher surface area. They can be kept in solution without signif-
icant sedimentation due to their Brownian motion. As the diameter
of the particle decreases, the melting temperature decreases as well.
This allows sintering at lower temperatures, which is beneficial for
substrates, especially polymer films. Therefore, nano Ni particles are
the interest of this research.
Conductive Ni inks are available in the market for screen printing
applications from different vendors and the range of bulk resistivity
is about 5 to 300 ohms/sq./mil. Nano Ni ink for inkjet and aerosol
applications is available, though the products are still in the experi-
mental phase. Ni ink for flexography and/or gravure printing has not
been studied yet.
The main substrates for PE are polymer films, paper/nano paper,
glass/flexible glass, wafers, metals and textiles. The substrates used for
graphic printings are less than ideal for printed electronic applica-
tions, due to their higher roughness in comparison to polymer films.
However, higher thermal stability of paper, in comparison to some of
the films, makes it more attractive for use. Therefore, there is a need
for more engineered paper substrates, specifically for PE applications.
Surface smoothness and substrate cleanliness are essential for PE.
Unevenness can cause the surfaces of printed conductive traces to be
uneven. This could create breaks and shortages in the circuitry. The
substrates have to be thermally and dimensionally stable, and chem-
ically compatible, in order to withstand the printing and sintering
processes of manufacturing. The glass transition temperature (Tg) of
the substrate—the temperature at which the substrate starts deform-
ing—has to be compatible with the processes as well.
Flexographic printing is used for flexible packaging significantly more
than gravure in North America and South America (see Figure 4).
Therefore, the purpose of this project is to formulate a water based
nano Ni conductive ink for flexo printing.
In general, inks are categorized according to their solvent component:
water based, solvent based, UV/EB based, soy based, etc. Solvent
based inks often contain enough organic solvents and volatile organic
compounds (VOCs) to be a concern environmentally. Water based
inks can also contain small amounts of VOCs with fewer environmen-
tal concerns. They are less flammable than solvent based inks, there-
fore they are easier to store and use. Water based inks have advantages
over solvent types, like their low evaporation rate, which allows them
to be more stable on the press without drying. They supply constant
viscosity in the ink fountain and doctor blade chamber.
The basic components of a conductive ink are functional pigments
that are used to give the needed electrical property; binders to help
ink to stick to the substrate; additives to add the needed performance
of inks, such as plasticizers, waxes, wetting agents, defoaming agents,
buffers and vehicle/carrier that are used to deliver ink onto the sub-
strate. However, in functional ink formulation, the use of binders and
additives should be as minimal as possible, since they negatively affect
the functional properties.
Most of the conductive inks must be sintered after they are printed on
a substrate. This can be accomplished by means of multiple processes
like drying, curing, reactive chemistry and annealing. Curing consists
of heating the inks to volatilize vehicle components. This allows the
Figure 4: Flexible packaging, by printing process and region
Data courtesy of DuPont Cyrel
28 FLEXO | MAY 2016
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