Investigation of Carbon Black Ink on Fine Solid Line Printing in ...
Transcript of Investigation of Carbon Black Ink on Fine Solid Line Printing in ...
Investigation of Carbon Black Ink on Fine Solid Line
Printing in Flexography
M.S.YUSOF; D.T.GETHIN
Welsh Center for Printing and Coating
Swansea University
Singelton Park SA2 8PP Swansea
UNITED KINGDOM
[email protected]; [email protected]
Abstract: - The flexographic printing process poses as an attractive candidate for printing electronics for its
high speed printing capabilities where such volume and large active areas need to be printed. Therefore an
investigation for its potential usage in printing electronics is highly in demand hence a research for suitable
conductive ink related to this process is vital. This paper will focus on a novel development of carbon black
ink in printing fine solid lines specifically developed for this type of printing method compared to commonly
used silver metallic filled inks and polymeric inks readily available in printing technologies which will also be
extensively reviewed and elaborated. A step by step approach by printing solid lines, measurements of printing
plates and printed images and finite element analysis (FEA) has been carried out in advance to help
comprehending this process that is influenced by many interacting parameters. Printing trials have also been
carried out in comparison with water based Panipol ink to check the compatibility and the suitability of the ink
developed for this printing technique.
Key-Words: - Flexography, printing solid line, waterborne carbon black ink, printing electronics
1 Introduction Electronic devices manufactured by printing are
likely to increase. The use of printing processes both
as impact and non-impact (i.e. ink jet) variants for
electronic products such as displays, back planes,
memory, antennas, batteries and other devices is
emerging because of the advances in material,
fundamental research related to the printing
processes and electronics design [1]. A significant
amount of research has been carried out on both
impact and non-impact printing to fulfill the
emerging demand of printing electronics. However,
impact printing processes are much faster and
capable of printing over large areas compared with
non-impact printing [2]. In impact printing, screen
printing has the advantages over other type of
printings and due to its capabilities to deposit thick
layers of ink over large areas [3]. It is currently
being used extensively and will continue playing a
leading role in printing electronic products.
However there are some disadvantages that include
speed where a high resolution web based
arrangement runs at only around 40m/min. And
although a web fed rotary screen can run at up to
150m/min regrettably this system is only capable of
lower resolution [4] and this limits the feature sizes
that may be printed. The alternative processes
comprise offset lithography, flexography and
gravure. These are all high speed processes that are
capable of high resolution printing achieving
typically 50µm [5] features for lines in the gravure
process compared with 20µm for flexography [6].
However, problems with electrical conductivity
remain and where a continuous solid line is vital.
The image shown in Figure 1 highlights such
potential discontinuity and this needs to be
addressed [7].
Figure 1: Gravure printed images
with jagged lines
The flexographic printing process offers the
possibility to print continuous fine solid lines [8].
While flexography is a simple process and the image
carrier is cheaper compared with gravure, a vast
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number of parameters affect this process which will
ultimately affect the quality of the printed images.
However, current research on printing plate
technology [9] and investigation into critical
parameters such as anilox rollers, ink rheology etc
[10, 11] help to comprehend the impact and the
affects of these and other parameters on the final
printed images. Further research on the application
of finite element analysis (FEA) including both
linear and non-linear models provides
complementary work to predict the printing plate
deformation [12] and in understanding the ink
spreading mechanism [13].
1.1 Conductive Inks Printing a conducting track is a vital requirement
for printing future electronic products. In printing
technologies there are a number of conductive inks
currently being considered. Commonly used are
inks with metallic particles such as silver, gold,
nickel and platinum. Also there are polymeric,
organic and inorganic conductive inks. In high
volume printing, there is a requirement for rapid
drying and the ability of the ink to adhere to the
substrate [14] or previously printed layer is
essential. In flexography, silver particle inks have
been explored [15-17], but these have served to
highlight the problem of the particulate filling the
engraving in the anilox.
Figure 2: 1500 lpi anilox cells on
Yag and CO2 aniloxes
Figure 3: Silver nanoparticle inks [18]
One of the reasons for this occurrence is the size of
the annilox cell opening which depend on the line
ruling and engraving shape. Using white light
interferometer measuring machine, a 1500 lines per
inch (lpi) ruling anilox has a cell opening of only
14µm across as seen in Figure 2 whereas the silver
flakes have a characteristic dimension in the range
of 10-20µm as shown in Figure 3.
The other concern is ink rheology. This is a delicate
balance between the mixture of particulate and
carrier fluid. A higher concentration of particulate is
desired for better electrical properties i.e reducing
resistance, but this can also lead to poor printability
as the flow viscosity no longer falls within the
process operating window. A few researchers have
explored conducting polymer inks, such as
Polyaniline [19-22]. The results from this point to
the fact that the electrical performance is not as
good as particle laden systems and that
environmental factors such as temperature and
humidity greatly affects the final results [23],
placing strict demands on the processing
requirements. Consequently alternative ink
formulations need to be considered, one of which is
based on a carbon system. Although carbon inks are
already available, little is known about the ink
formulation that is often subject to commercial
confidentiality. In this work a carbon ink was
formulated that used water as the main carrier fluid.
The formulation comprised of carbon beads and
water, solvent for quick drying, additives or
surfactant as bubble deformer and acrylic styrenated
self-crosslinking copolymer dispersion to enhance
the adhesion of the inks to the ink carrier and onto
the substrtates. This ink formulation was tested in
this research to identify its printability in exploring
the feasiblity to be used as conductive inks. This
will be described in the following sections.
2 Experimental and Results In this study, carbon black beads were used and
milled using a milling machine as shown in Figure
4. Also in this research, the experiments were
carried out under normal room temperature and kept
constant avoiding further variables.
Figure 4: Netzh beads milling
machines
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Ink formulations were then carried out where the
grained carbon beads were mixed with the
formulation described earlier. The particle size
within the ink was measured using a Hegman gauge
from which it was determined that a particle size
ranging between 2 and 4µm was achieved. Based on
the previous experiments, the size of the particle
inside the inks should be typically three or more
times smaller than the anilox cell opening. The
viscosity of the carbon black ink was compared to a
UV graphic ink that is known to work well on a
flexographic press. Substrate suitability needs to be
established and this has been performed using
deionised water as this is a dominant component
within the ink. This was established using a
dynamic contact angle measurement device and a
number of candidate substrates were tested as shown
in Figure 5.
Figure 5: Water contact angle on various
substrates
The data shown demonstrates that a BOPP
(Biaxially Oriented PolyPropylene) with corona
treatment is a suitable substrate as it is impermeable
and has favourable wetting characteristics, denoted
by the lowest value of contact angle.
The formulated carbon black ink was then compared
to a non-engineered waterborne Polyaniline ink
which has been specifically designed for offset and
flexographic printing obtained commercially. The
surface tension of both inks and its printing
compatibility on the BOPP substrate was tested and
the results are shown in Figure 6.
Figure 6: Surface Tension of carbon
black and PANI
Observations show that the carbon black ink has a
lower surface tension than the polyaniline
counterpart, indicating that it spreads better on the
substrate. Further analyses on the contact angle as
shown in Figure 7 points to the fact that the carbon
black is likely to be better than the polyaniline
counterpart when printed on this substrate. It
demonstrates that it will be more successful in
wetting the substrate and consequently adhering to it
when it is dry.
Figure 7: Contact angle of
conductive inks on BOPP
A series of experiments on a bench press printer
were also carried out to test these conductive inks
more rigorously in terms of their printability. A
successful printed images using carbon black ink
can be seen in Figure 8. This was achieved under the
10N impression pressure and the multiple line shows
a successful print of 50µm line width with a 100µm
line gap. However an attempt to print waterborne
PANI is unsuccessful due to high surface tension
with this type of substrate.
A series of experiments on a bench press printer
were also carried out to test these conductive inks
more rigorously in terms of their printability. A
successful printed images using carbon black ink
can be seen in Figure 8. This was achieved by using
a bench lab printer (IGT-F1) with 10N load
engagement and 600 lpi aniloxes. The multiple lines
show a successful print of 50µm line width with a
100µm line gap (on the right hand side). However
an attempt to print waterborne PANI is unsuccessful
due to high surface tension with this type of
substrate.
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Figure 8: Printed images of carbon
black using IGT-F1 bench printer
4 Conclusion It is clear that the newly formulated waterborne
carbon black ink is suitable for printing carbon
tracks that exhibit a continuous structure,
eliminating process failure through drying in the
anilox. From the data obtained on the printed
images, it shows that a homogeneous layer of carbon
black ink could be deposited on thin film flexible
substrate of BOPP. It also clearly shows excellent
stability where there is no sign of pigment settling,
pigment kick-out, surface colour floatation, liquid
phase separation or any gellation after the ink has
dried under ambient temperature. However the
downside of this printing method is the ink film
thickness were only between 5µm - 7µm could be
deposited which may lead to a very high resistance
if used as conductive tracks. Consequently, further
research on this waterborne carbon black ink is
required with a view to improving its electrical
performance while not compromising its printing
performance. A comparison of the two ink results
reveals that engineered inks are needed and works
better compared to a non engineered inks depending
on the circumstances as comented by Commerford.
Nonetheless, it shows that it could be utilized as
passive RFID antennae in close range of few meters
proximity are feasible with the advantage of
flexographic printing process of fast reproduction
and at a very low cost.
References:
[1]Kleper, M.L., Printed Electronics and the
Automatic Identification of Objects. 2004:
GATF Press. 63.
[2]Kippan, H., Handbook of Print Media. 2001,
Berlin-Heidelberg: Soringer-Verlag
[3]Blayo A, Pineaux B. Printing Processes and
their Potential in Printing RFID in Proceedings
Smart Objects and Ambient Intelligence 2005,
France
[4]Rigney, J. Materials and Processes for High
Speed Printing for Electronic Components. in
International Conference On Digital. Michigan,
USA. 2004.
[5]D.Gamota, P.B., K.Kalayasundram, J.Zhang,
Printed Organic and Molecular Electronics.
Massachusets 2004,: Kluwer Academic
Publishers.
[6] M.S.Yusof, T.V.K., F.M.Jachim, T.C.Claypole,
D.T.Gethin. Fine Line Printing for the
Reproduction of Electrical Devices by
Flexography. in Technical Research Conference.
2006. Swansea University.
[7]M.S.Yusof, T.C.C., D.T.Gethin. Fine Line
Printing by Flexography Printing. in ESPRC
International Colloquium on Integrated
Manufacture by Printing Greygynog, UK. 2006.
[8]M.S.Yusof, S.M.H., T.C.Claypole, D.T.Gethin.
Investigation into Ultra Fine Solid Lines in
Flexographic Printing. in Malaysian Research
Group International Conference.Salford, UK.
2006
[9]M.S.Yusof, S.M.H., T.C.Claypole, D.T.Gethin.
Measuring Solid Line Geometry on Flexographic
Photopolymer Printing Plate. in International
Conference on Print and Media Technology.
Chemnitz, Germany, 2005.: Verlag fur
Wissenschaft und Fochung, Berlin.
[10]M.S.Yusof, A.M.A.Z., T.C.Claypole,
D.T.Gethin. The Effects of Anilox Roller on Fine
Line Printing in Flexographic Printing Process.
in 2nd International Conference on Print and
Media Technology. 2007. Chemnitz, Germany:
Verlag fur Wissenschaft und Forschung, Berlin.
[11]M.S.Yusof, A.M.A.Z., T.C.Claypole,
D.T.Gethin. The Effects of Printing Plate on the
Reproduction of Fine Solid Line Printing in
Flexography. in 2nd International Conference on
Print and Media Technology. Chemnitz,
Germany 2007.: Verlag fur Wissenschaft und
Forschung, Berlin.
[12]M.S.Yusof, T.C.C., D.T.Gethin. Exploring Fine
Line Reproduction in Flexography. in 2nd
International Colloqium on Integrated
Manufacture by Printing,. Greygynog, UK.
2007.
[13]M.S.Yusof, T.V.K., T.C.Claypole, D.T.Gethin.
An Investigation into Deformation of
Photopolymer Plate During Printing Solid Lines
in Flexography. in 5th European Conference on
Contitutive Models for Rubber.. Paris, France:
2007 Taylor & Francis.
[14]Jay Sperry, E.W., Conductive Inks and In-line
Flexo; An Investigation of Process Benchmarks
for RFID Printing, in Flexo Magazine. 2005.
Recent Researches in Communications, Automation, Signal Processing, Nanotechnology, Astronomy and Nuclear Physics
ISBN: 978-960-474-276-9 141
[15]Hrehorova, E., Wood ,, L. K., Pekarovic, J.,
Pekarovicova, A., Fleming, P. D. , and Bliznyuk,
V. The Properties of Conducting Polymers and
Substrates for Printed Electronics. in IS&T
Digital Fabrication. Baltimore, USA:
http://www.imaging.org/conferences/DF/. 2005
[16]Sangoi, R.S., C. G. Seymour, M. D.
Venkataraman, J. N. Clark, D. M. Kleper, M. L.
Kahn, B. E. , Printing Radio Frequency
Identification (RFID) Tag Antennas Using Inks
Containing Silver Dispersions in Journal of
Dispersion Science and Technology,Vol. 25(4):
2004 p. 513-522.
[17].G.Scmidt, H., Hann, Fugman. Realization of
Electronic Structures by Means of Flexographic
Printing. in International Conference on Print
and Media Technology. Chemnitz,Germany;
Verlag fur Wissenschaft und Fochung, Berlin.
2005.
[18]Cloud C, The 8 Most Unusal and Curtting Edge
Inks, Availables from
http://www.cartridgesave.co.uk/news/the-most-
unusual-cutting-edge-inks 2009
[19]Tapio Mäkelä, T.H., Päivi Majander and Jouni
Ahopelto. Novel Imprinting Tool for Roll to Roll
Manufacturing of Submicron Structures. in TNT
"Trends in Nanotechnology", Oviedo, SPain:
http://www.phantomsnet.net/. 2005
[20]Tapio Mäkelä, S.J., ]H.Kosonen, T.G.
Backlund, H.G.O. Sanberg and H. Stubb,
Utilizing Roll-To-Toll Techniques for
Manufacturing Source-Drain Electrodes for All
Polymer Transistors, in Science Direct. 2005. p.
285-288.
[21]Karwa, A., Printing Studies with Conductive
inks and Exploration of New Conducting
Polymer Compositions, in Center for Materials
Science and Engineering, Rochester Institute of
Technology: New York. 2006 p. 94.
[22]May, K.W. Conductive ink based page
detection for linking digital and physical pages.
in Conference on Human Factors in Computing
Systems 2001. Seattle, Washington ACM New
York, NY, USA
[23]Marko Pudas, J.H., Seppo Leppävuori, Gravure
Offset Printing of Polymer Inks for Conductors.
Progress in Organic Coatings,. Vol. 49(4): 2003
p. 324-335.
[24]Comerford R, Conductive Ink, flex plates print
RF anntennas on cardboard in POWEREX (Ed);
Electronic Products 2006
[2] X2. Author, Title of the Book, Publishing House,
19XX
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ISBN: 978-960-474-276-9 142