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Conductive,
Transparent,
Flexible
Films. Transparent, conductive films
based on flexible plastic sheets open up
completely new designs for control and
touch-keys. These “invisible” touch-keys
can be integrated into transparent user
interfaces or into curved (3-D) surfaces.
This allows decoration and functionality
to be combined with maximum design
flexibility, e. g. in cars and smartphones.
Transparent conductive films
with structured conductors
(photo: PolyIC)
MARTIN SCHEWE
HENNING ROST
lexible, optically transparent films
are required for applications such as
displays, ultra-thin heating elements, and operating controls in automobiles. They must have a coating that possesses the maximum-possible electrical
conductivity. Nowadays, polyester-based
plastic films coated with indium tin oxide (ITO) are often used, but these are
technically difficult and expensive to
structure prior to use [1]. The limited
conductivity and relative fragility of ITO
renders it less suitable for applications involving large and, especially, curvaceous
surfaces.
F
Translated from Kunststoffe 10/2012, pp. 38–42.
Article as PDF-File at www.kunststoffe-international.com; Document Number: PE111174
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Alternatives to ITO technology that do
not have these disadvantages are now
available in the marketplace. Thus, PolyIC GmbH & Co. KG, Fürth (a member of
the Kurz Group) has succeeded in creating a low-cost, high-volume roll-to-roll
production process (Fig. 1) for printed electronics and thus also in developing transparent, conductive films.
The overall process of manufacturing
printed electronics relies heavily on the
production of electrodes and conductors
– i. e. of conductive structures. These
structures are so fine that they cannot be
detected by the human eye unaided.Aside
from high conductivity, the creation of
high-resolution, micron-size structures
on thin, flexible polyester films (the typical resolution is 10 microns) can lead to
highly transparent layers. Consequently,
these are very appealing interesting for
applications which were previously the
preserve of ITO-coated films, but which
suffered from the familiar disadvantages.
The degree of transparency and conductivity can be customized by varying
the coverage of the surface (width and
density of the conductive structures per
m2 polyester film) with conductive material. The latter are metals which, in line
with the application, are applied over the
full length and breadth of the film or as
an individual layout in the form of a pattern (see [4] for technical details).
i
Contact
PolyIC GmbH & Co. KG
D-90763 Fürth
Germany
TEL +49 911 20249 8145
> www.polyic.com
© Carl Hanser Verlag, Munich
Kunststoffe international 10/2012
Electronics
SPECIAL
Fig. 1. Flexible, conductive and transparent films on the machine
The most popular carrier material is
polyethylene terephthalate (PET), because
it can be obtained in thin, flexible, highly
transparent grades and in bulk. Added to
which, in comparison to other plastics, it
is relatively inexpensive. Flexible, conductive and transparent films are offered by
PolyIC under the name PolyTC. They
serve as a widespread replacement for ITO
in various sensor elements, such as
touch-screens and
touch-keys
(Title picture).
Other application areas for PolyTC
films are:
transparent EMI shielding films,
transparent heating films,
transparent electrodes for organic light
emitting diodes (OLEDs) and organic
solar cells (organic photovoltaics or
OPVs), as well as
electrostatic discharging (ESD).
(figs. 1 to 3: PolyIC)
Transparent Films for
Touch-keys
Touch-keys are electronic switches which
contain no moving mechanical parts and
are operated by the touch of a finger. They
are currently the main application for
transparent conductive films. Touch-keys
are composed of conductive surfaces
which are connected to controller chips.
These devices detect changes which occur in electrical capacitance when, for example, a finger touches the film. Such a
change triggers a switching operation.
Eliminating mechanical parts renders the
touch-keys very rugged. Furthermore,
they are easy to integrate into all kinds of
applications because they are flat and have
hardly any bulk. Their transparency allows them to be used as discreet switches
which become visible only when they are
>
back-lit.
Fig. 2. Transparent
conductive films for
touch-keys
Kunststoffe international 10/2012
www.kunststoffe-international.com
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SPECIAL
Touch-keys made with PolyTC films
have obvious advantages. They
are transparent,
can be back-lit,
are thin and flexible and so can be incorporated into curved surfaces,
have no mechanical components at all
and are subject to little wear,
could be used wherever easy-clean surfaces or switches are needed, e.g. in the
medical field.
Touch-keys open up new, innovative design concepts that have clear technical advantages to offer. Aside from vehicle cabins, conceivable applications are button
panels (Fig. 2) for white goods (large electronic domestic appliances such as stoves,
refrigerators and washing machines),
brown goods (electrical or electronic consumer goods such as televisions, radios,
and DVD players), and medical devices.
Their flexibility is an advantage which
should not be underestimated. Until recently, conventional touch-keys could be
integrated into flat, even surfaces only.
Now, those based on PolyTC films can be
Fig. 3. Flexible, conductive and transparent films in swept or curved surfaces (e.g. dashboards)
a single step. This process can slash the
cost of production because the plastic
parts are already fully decorated at the injection stage. This means that there is no
need for a decoration step after injection
molding, or for interim storage and additional steps. This process also facilitates
to use the PolyTC film in the fabrication
of decorative plastic parts with integrated touch functionality by means of an injection molding process and a combination of IMD and IML. The visible surface
of the component is not blocked by mechanical switches as a result, because the
switching elements are located behind the
decoration. Non-conductive metallic
IMD films can be used to produce metallic or even brushed-metal surfaces with
active buttons.
Electrodes for EMI Shielding
Electromagnetic interference (EMI)
refers to electronic emissions which interfere with an electronic device or which
the device itself produces. The growing
complexity of electronic circuits, e.g., in
the automotive sector and in mobile telephony, means that interference by electromagnetic waves is becoming more
common. The use of components that fall
into the EMI shielding category can contain this risk. PolyIC can produce highly
transparent, conductive PolyTC films for
shielding electromagnetic interference in
displays (Fig. 4).
Such films offer the following benefits
for EMI shielding:
customized layouts in the form of
rhombic, rectangular or hexagonal designs
individually controlled surface resistance with appropriate shielding effect
and desired transparency, and
!
Fig. 4. Possible applications for flexible, conductive and transparent films
incorporated anywhere on the dashboard
or center console – even swept and curved
areas, opening up scope for novel, creative
and elegant designs that have no mechanical switches or buttons (Fig. 3).
Active Buttons
Furthermore, combining decorative film
technology and functional film, i.e. PolyTC, leads to radically new design possibilities. Recently, in-mold decoration
(IMD) has become the established
method of decorating plastic parts (injection of individual films or labels is called
in-mold labeling (IML)). IMD combines
injection molding and hot embossing in
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(photo: iStock)
Electric Heating Elements
The conductors on the PolyTC films can
also be made to convert electrical power
into heat so that these can serve as heating films. Although high resolution of the
PolyTC structures leads to high transparency values, it also lowers the conductivity of the film, and so heat output is
limited. Consequently, when a PolyTC
heating film is being designed, a good
compromise between adequate transparency and sufficiently high conductivity needs to be found. Nevertheless, the
films described here offer potential for use
in local heating elements, e.g. preventing
fogging of windshields and car mirrors.
Printed Electronics
Printed electronics is a set of printing
processes for wholly or partly creating
electronic devices. Unlike conventional
printing inks, which have no electrical function whatsoever, these processes print
electronically functional materials, often in
the form of specialty polymers. These conducting, semi-conducting and insulating
polymers are dissolved in common organic
solvents and printed as a kind of electronic
ink [2]. Various layers of the polymers are
deposited on each other with great precision to create a structure. Electronic devices such as transistors, diodes and capacitors can be fabricated in this way [3].
The use of modern, high-volume printing
methods significantly lowers the manufacturing costs. The ability to print large-area
and flexible substrates and the use of novel
functional materials open up electronics
applications, to which conventional siliconbased electronics had little or no access.
New developments made possible by printed electronics include such applications as
radio frequency identification tags (RFID
tags), flexible displays and solar cells.
© Carl Hanser Verlag, Munich
Kunststoffe international 10/2012
Electronics
SPECIAL
cations on the mass market. The first
product of this type, namely conductive
and transparent films based on PolyTCbrand plastics, is of course for practical,
high-volume applications. This novel film
offers clear advantages both in terms of
product design and integration into the
target product. REFERENCES
1 Wörle, J.; Rost, H.: Roll-to-roll production of transparent conductive films using metallic grids. MRS
Bulletin 36 (10) (2011) p. 789
2 Rost, H.: From Polymer Transistor to Printed
Electronics. Kunststoffe international 10 (2005)
pp. 209–214, PE103333
3 Rost, H.; Mildner, W.: On the Way to Printed Electronics: Latest Advances. Kunststoffe international 6 (2008) pp. 60–64, PE104275
4 Wörle, J.; Rost, H.: Invisible Helpers: Conductive
Films. Kunststoffe international 4 (2010)
pp. 58–61, PE110369
5 www.occhio.de
THE AUTHORS
MARTIN SCHEWE, born in 1981, is Project Manager at PolyIC GmbH & Co. KG, Fürth, Germany;
[email protected]
DR. HENNING ROST, born in 1966, is Senior Project Manager at PolyIC GmbH & Co. KG.
Fig. 5. Gesture-controlled lamp featuring a
flexible, conductive and transparent film
incorporated into the lens of the lamp head
(photo: Occhio)
customer-specific geometry for the
desired EMI cut-off frequency.
Light Elements Controlled by
Gestures
At the 2012 Light+Building Show in
Frankfurt am Main, Germany, Occhio
[5], the a German lighting manufacturer, presented an innovative new
lighting series called ìo 3d.
The extraordinary thing about this
lighting system is not just the design,
but the new and innovative operating
concept. Instead of conventional
switches and buttons, it is operated by
simple hand gestures: contactless and
intuitively. Moving a hand toward the
top of the light makes it brighter or
dimmer. A quick flick of the hand at
the top switches it on and off.
Inside the Occhio lamp, the PolyTC film is integrated into the lens of
the lamp head where it acts as the sensor for contactless gesture control. It
utilizes the so-called proximity effect
to detect an approaching hand, and
then translates the gesture into the appropriate command (Fig. 5).
Conclusion
Printed electronics – that is, the production of electronic components
and products by roll-to-roll processes – has left the laboratory behind and
notched up its first successful appliKunststoffe international 10/2012
www.kunststoffe-international.com
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