Investigation of Carbon Black Ink on Fine Solid Line Printing in Flexography …wseas.us/e-library/conferences/2011/Cambridge/NEHIPISIC/... · 2011-03-01 · nonimpact printing [2]

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

Recent Researches in Communications, Automation, Signal Processing, Nanotechnology, Astronomy and Nuclear Physics

ISBN: 978-960-474-276-9 138

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


ISBN: 978-960-474-276-9 139

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.


ISBN: 978-960-474-276-9 140

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.


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


ISBN: 978-960-474-276-9 142

Documents

Investigation of Carbon Black Ink on Fine Solid Line Printing in Flexography …wseas.us/e-library/conferences/2011/Cambridge/NEHIPISIC/... · 2011-03-01 · nonimpact printing [2]