Deliverable 11.11 – Single pass inkjet printing system
Confidential 1
Deliverable 11.11 – Demonstration of single pass in kjet
printing system
Date: 11th August 2015
Author: Michael Graf
Research & Development Department
Durst Phototechnik Digital Technology
GmbH
9900 Lienz, Austria
Deliverable 11.11 – Single pass inkjet printing system
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Table of content
1. INTRODUCTION ....................................................................................................................................... 3
2. DETAILED INVESTIGATION OF SUITABLE INDUSTRIAL INKJET PRINTHEADS .................................................. 5
2.1. INTRODUCTION ................................................................................................................................................ 5
2.2. BASIC PRINTHEAD EVALUATION ........................................................................................................................... 6
2.3. INTEGRATION OF MULTIPLE PRINTHEADS INTO SINGLE PASS SYSTEM ............................................................................ 9
2.4. CONCLUSION ................................................................................................................................................. 10
3. SINGLE PASS INKJET PRINTING SYSTEM – MECHANICS AND IMPLEMENTATION ........................................ 11
3.1. CARRIAGE AND SUPPORT ................................................................................................................................. 12
3.2. VACUUM CONVEYOR BELT SYSTEM .................................................................................................................... 13
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1. Introduction
Thanks to its versatility inkjet printing has gained a lot of interest as a cost efficient
replacement for established analogous printing and production techniques in different
industries. Moreover in the last two decades it has been shown that it is possible to
develop functional inkjet processable fluids which after film formation and post treatment
lead to the needed functionalities for a lot of different applications, for example
numerous sub processes in the microelectronics industry. However the conversion from
conventional analogous techniques towards inkjet and especially the industrial
implementation very often is challenging due to the complexity of inkjet technology. The
basic concept of droplet generation is given by the natural instability of a liquid jet which
is a complex surface tension driven process. In high throughput industrial single pass
printing systems millions of microscale droplets are generated every second. The
precise control of droplet generation and the overall process for accurate placement of
each droplet on the substrate is of major importance. The mentioned overall process can
be represented by the so called magic triangle of inkjet which is shown in Figure 1.
Figure 1: Magic triangle of inkjet consisting of pr inthead, ink and substrate
The magic triangle is defined by the main components of an inkjet process which are
printhead, ink and substrate and the interaction between them. For each application the
right main components have to be chosen and the precise adjustment of their interaction
is crucial for a reliable high quality printing process.
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Within the ML2 project and the underlying idea of roll to roll production of multilayer
microlabs different sub processes where inkjet printing could be an efficient production
technique can be identified. These sub processes are:
� Printing of conducting paths onto thin plastic films (PET, PMMA, OPP etc.) for
heterogeneous implementation together with pick and place. Therefore nano
particulate silver and copper dispersions should be used.
� Precise deposition of bio-chemical reagents such as for example antibodies
� Deposition of adhesives to prevent blocking of micro fluidic structures during
lamination
� Printing of microlenses for use with planar light guide structures
As already mentioned each layer of the multilayer devices should be treated in a roll to
roll process. In order to have a complete inline production process with an implemented
inkjet printing system a single pass printing process is needed which should be able to
handle flexible (thin foils with a thickness down to 50µm) as well as rigid media
(laminated stack of multiple layers). The production line and therefore the inkjet printing
system should be able to handle media widths up to 600mm although in a first step the
printing width is limited to 300mm (just 300mm equipped with printheads). Although the
single pass inkjet printing system is able to handle line speeds up to 60m/min, the
targeted overall line speed is limited to 10m/min due to production processes such as
embossing. The single pass inkjet printing system contains three bars with printheads to
be able to handle three different fluids.
The above mentioned possible applications of inkjet printing within the ML2 project have
different requirements in terms of jetting, integration of the fluidic system and post
treatment of the printed films. The single pass inkjet printing system has been designed
to meet these requirements by a detailed evaluation of core components which will be
described in the following chapters.
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2. Detailed investigation
2.1. Introduction
As already described in chapter
inkjet printing system and the careful selection of the right printhead and t
tuning of the interaction between printhead and fluid is of major importance to achieve a
reliable high quality printing process.
the ML2 project, are often prone to sedimentation
caused by volatile solvents
process. Single pass printing does not allow cyclic maintenance such as spitting and/or
purging and therefore printheads with recirculation at
these continuous fluid recirculation prevent loss of reliability.
industrial piezo drop on demand inkjet printheads from different manufacturers are
available but just Fujifilm Dimatix and Xaar
recirculation at nozzleplate level
Dimatix printheads are robust and moreover very precise products which
towards accurate and reliable single pass pr
evaluate two different piezo drop on demand inkjet printheads based on silicon MEMS
technology from Fujifilm Dimatix.
Table 1 : Comparison of two different Fujifilm Dimatix piez o
based on silicon MEMS technology with integrated fl uid recirculation on nozzle plate level
Fujifilm Dimatix SAMBA G5L
� Silicon MEMS
technology
� 2048 Nozzles
rows
� 1200dpi native
resolution
� Native Drop Size
5pl
Deliverable 11.11 – Single pass inkjet printing system
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Detailed investigation of suitable industrial inkjet printheads
As already described in chapter 1 the printheads are one of the core components of an
inkjet printing system and the careful selection of the right printhead and t
tuning of the interaction between printhead and fluid is of major importance to achieve a
reliable high quality printing process. Functional fluids, which should be printed within
project, are often prone to sedimentation, gelation and/or
and these effects have an impact on reliability of the printing
process. Single pass printing does not allow cyclic maintenance such as spitting and/or
and therefore printheads with recirculation at nozzleplate level are needed
continuous fluid recirculation prevent loss of reliability. A lot of different types of
industrial piezo drop on demand inkjet printheads from different manufacturers are
lable but just Fujifilm Dimatix and Xaar offer printheads with continuous fluid
ozzleplate level. Thanks to their silicon MEMS technology the Fujifilm
Dimatix printheads are robust and moreover very precise products which
towards accurate and reliable single pass printing processes. Therefore we decided to
evaluate two different piezo drop on demand inkjet printheads based on silicon MEMS
technology from Fujifilm Dimatix.
: Comparison of two different Fujifilm Dimatix piez o drop on demand inkjet printheads
based on silicon MEMS technology with integrated fl uid recirculation on nozzle plate level
Fujifilm Dimatix SAMBA G5L Fujifilm Dimatix QSRJM 256/10
Silicon MEMS
technology
2048 Nozzles, 32
rows
1200dpi native
resolution
Native Drop Size
5pl
Single pass inkjet printing system
5
inkjet printheads
the printheads are one of the core components of an
inkjet printing system and the careful selection of the right printhead and the exact fine
tuning of the interaction between printhead and fluid is of major importance to achieve a
, which should be printed within
d/or drying processes
an impact on reliability of the printing
process. Single pass printing does not allow cyclic maintenance such as spitting and/or
nozzleplate level are needed. In
A lot of different types of
industrial piezo drop on demand inkjet printheads from different manufacturers are
offer printheads with continuous fluid
Thanks to their silicon MEMS technology the Fujifilm
Dimatix printheads are robust and moreover very precise products which are tailored
inting processes. Therefore we decided to
evaluate two different piezo drop on demand inkjet printheads based on silicon MEMS
drop on demand inkjet printheads
based on silicon MEMS technology with integrated fl uid recirculation on nozzle plate level
Fujifilm Dimatix QSRJM 256/10
� Silicon MEMS
technology
� 256 Nozzles,
single row
� 100dpi native
resolution
� Native drop
size 10pl
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Looking at the two dimensional printhead design space spanned by the ink viscosity
range for reliable jetting and the native drop size of the printhead these two drop ejectors
cover different areas as can be seen in Figure 2. Figure 2 also indicates the location of
the possible ML2 applications.
Figure 2: Depiction of the printhead design space s panned by ink viscosity and native drop size
and indicated positions of possible applications wi thin ML 2; Yellow area covered by QSRJM 256/10
and orange area covered by SAMBA
It can clearly be seen in Figure 2 that the areas covered by the two printheads within the
printhead design space have a good overlap with respective two ML2 applications.
2.2. Basic printhead evaluation
Droplet generation with a piezo drop on demand inkjet printhead is a multistage process
where multiple energy conversions from electrical energy to the point of kinetic energy of
the microscale droplet take place. A detailed understanding of the physics behind these
processes especially the acoustic phenomena within the microfluidic channels of each
droplet ejector is of major importance for gaining reliability. For that reason the idealised
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jetting performance of both printheads under lab conditions was investigated. Therefor a
JetXpert drop visualisation system was used which is shown in Figure 3.
Figure 3: Image of a drop visualisation system from ImageXpert ( www.jetxpert.com )
At first the hydrodynamic behaviour of the fluid recirculation inside the printheads was
evaluated. Especially the hydraulic resistance of the printhead was of interest.
Additionally to experiments a simple mathematical model was developed and the output
was compared to measurement results. Figure 4 shows an example of the measured
and calculated fluid flow rate versus pressure difference between inlet and outlet port for
one of the two printheads. The graph shows a good agreement between model and
measurement.
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Figure 4: Measured and calculated fluid flow rate v ersus pressure conditions at the inlet and outlet
port of the printhead
Measurement and calculation were in good agreement for both printheads. This can also
be seen in Figure 4.
For piezo drop on demand printheads droplet generation results from applying an
electrical signal to a piezo actuator which changes its shape as a response to the
electrical signal. This change in the outer dimensions of the piezo actuator induces a
pressure wave inside a microfluidic channel. Due to the complex geometry of the
microfluidic channels inside the printhead, which is a composite of different materials,
the pressure wave is reflected multiple times resulting in complex acoustic phenomena.
When measuring drop velocity at different frequencies the channel acoustic can clearly
be seen.
0
2
4
6
8
10
12
14
0 50 100 150 200 250
flo
w r
ate
(m
l/m
in)
pressure difference (mbar)
Flow rate calculated Flow rate measured
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Figure 5: Sequence of d rop visualisation
30kHz
The applied voltage in most cases
microseconds and the exact timing within a single trapezoid pulse and moreover a
sequence of pulses is crucial
detail and the shape of applied voltage was optimised for reliable jetting.
2.3. Integration of multiple printheads into single pass system
For single pass printing the ability for easy integration of the printheads into print
modules and furthermore into print bars
print modules the jetting performance of the printheads in the stitching area
controlled and strategies to avoid
missing jets have to be developed. Therefore
strategies were evaluated and printing tests on a roll to roll lab system were pe
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rop visualisation system image s at printing frequencies from 1kHz to
ied voltage in most cases has trapezoid shape wit
microseconds and the exact timing within a single trapezoid pulse and moreover a
is crucial. For both printheads channel acoustic was investigated in
plied voltage was optimised for reliable jetting.
Integration of multiple printheads into single pass system
For single pass printing the ability for easy integration of the printheads into print
modules and furthermore into print bars is very important. When aligning printheads into
the jetting performance of the printheads in the stitching area
controlled and strategies to avoid and/or hide defects like wood grain pattern and
missing jets have to be developed. Therefore different module designs and alignment
strategies were evaluated and printing tests on a roll to roll lab system were pe
Single pass inkjet printing system
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s at printing frequencies from 1kHz to
trapezoid shape with pulse widths of
microseconds and the exact timing within a single trapezoid pulse and moreover a
oth printheads channel acoustic was investigated in
plied voltage was optimised for reliable jetting.
Integration of multiple printheads into single pass system
For single pass printing the ability for easy integration of the printheads into print
is very important. When aligning printheads into
the jetting performance of the printheads in the stitching area has to be
defects like wood grain pattern and
different module designs and alignment
strategies were evaluated and printing tests on a roll to roll lab system were performed.
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Figure 6: Image of multiple Fujifilm Dimatix QSRJM 256/10 printheads aligned in a print module
with integrated fluidic and electrical interface
These experiments gave promising results for both printheads although the limits of the
QSRJM 256/10 printhead technology in terms of integration into the single pass inkjet
system could be seen.
2.4. Conclusion
Two different industrial piezo drop on demand inkjet printheads from Fujifilm Dimatix
were evaluated which are SAMBA and QSRJM 256/10. Both are robust industrial
products with integrated ink recirculation at nozzle plate level based on silicon MEMS
technology. Main focus of the investigation was to get a detailed understanding of the
strengths and weaknesses of both printheads in terms of fluid recirculation, jetting
performance and integration into the single pass inkjet system. After detailed analysis of
all available data and also including commercial aspects we came to the conclusion that
the SAMBA technology fits best for the requirements within the ML2 project. The main
reason is that it’s a very compact high resolution printhead which is easily scalable to
any print width. The native resolution of 1200dpi allows easy compensation for missing
or deviated jets. Moreover from commercial point of view it’s the most cost effective
solution which fulfils the requirements within the project.
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3. Single pass inkjet printing system – mechanics a nd implementation
As described in chapter 1 the magic triangle of inkjet printing is defined by three main
components. One of these are the printheads and the process which led to the decision
which industrial piezo drop on demand printhead fits best for the requirements of the
ML2 project is described in chapter 2. Nevertheless in a real industrial printing process
more is needed than just precise adjustment of printing parameters on stationary
printheads. Because of printhead maintenance and height adjustment due to variable
thickness of the substrates the printheads have to be moved in two dimensions. Another
main component of the magic triangle is the media and media handling system. The
movement of the substrate underneath the printheads is done by a vacuum conveyor
belt system which is able to handle flexible and rigid media. Figure 7 and Figure 8 show
a CAD drawing and a photographic image of the ML2 single pass inkjet printing system.
Figure 7: CAD Image of the ML 2 single pass inkjet printing system without casing, printheads and
ink management system
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Figure 8: Photographic image of the single pass ink jet printing system
3.1. Carriage and support
The printheads will be mounted on a carriage which can be moved in two dimensions.
Figure 9 and Figure 10 show a CAD drawing of the carriage and the support which
holds the carriage and a photographic image thereof respectively.
Figure 9: CAD drawing of the carriage and the suppo rt which holds the carriage
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Figure 10: Photographic image of the carriage and t he support
The z – movement of the carriage is done by a stepper motor with integrated encoder
with a maximum travelling distance of 180mm. The support contains a rail system which
allows the x – movement of the carriage for maintenance. In that direction it is driven by
a linear motor which allows precise adjustment of the position. All axes including the
vacuum conveyor belt are controlled by a Beckhoff automation system and accessible
via touch panel.
3.2. Vacuum Conveyor belt system
One of the main components of the single pass inkjet printer is the media handling
system. As already mentioned the single pass inkjet printing system has to be able to
handle rigid and flexible media. Therefore a high precision vacuum conveyor belt system
was designed which fulfils the requirements of the ML2 project. Due to the fact that the
media handling system has a big impact on possible printing accuracy it has to be very
well engineered and strategies to optimise velocity uniformity and minimise drift of the
belt have to be developed.
Figure 11 shows a CAD drawing (left) and a photographic image of the conveyor belt
system.
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Figure 11: CAD drawing (left) and photographic ima ge of the conveyor belt system
The belt of the current system is made of a polyester mesh with polyurethane topcoat
and has a width of 800mm. The overall system is designed in a way that also a stainless
steel belt could be used. A slightly decreased pressure in a vacuum chamber
underneath the belt, which has punched holes with a diameter of 2mm, fixes the
substrate at the required position. Figure 12 shows a CAD drawing of the belt with
punched suction holes.
Figure 12: CAD drawing of the belt with suction hol es
Extensive tests with 50µm PMMA sheets were performed to ensure that the distortion of
the thin substrates through the cross sectional area of the punched holes does not have
a negative influence on the printed image. These tests clearly showed that this is not the
case.
Suction holes
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The conveyor belt system is driven by a servo asynchronous motor (nominal torque
6,7Nm) with coupled planetary gear which allows a maximum linear belt speed of
60m/min. Measurements of velocity uniformity clearly showed that at a linear speed of
1m/s the maximum variation is 1mm/s.
For precise control of the belt position on the rollers and for preventing a belt movement
in cross process direction an active belt control system is implemented. It consists of a
tensioning roller which forces a tension gradient to the belt and this leads to a controlled
movement in cross process direction. The actual position of the belt on the rollers is
measured by a laser micrometer which is triggered by a light barrier to be able to always
measure at the same position. It can be shown that the maximum belt movement in
cross process direction is less than 100µm over one passage (which corresponds to
8,5m) at a speed of 60m/min.