deliverable 11.11 demonstration of single pass inkjet printing … · 2017-04-25 · avai lable but...

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


Confidential 2

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


Confidential 3

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.


Confidential 4

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.

Deliverable 11.11

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


Confidential

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


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


and therefore printheads with recirculation at nozzleplate level are needed

continuous fluid recirculation prevent loss of reliability. A lot of different types of


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


technology from Fujifilm Dimatix.

: Comparison of two different Fujifilm Dimatix piez o drop on demand inkjet printheads


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


, which should be printed within

d/or drying processes

an impact on reliability of the printing


nozzleplate level are needed. In

A lot of different types of


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


drop on demand inkjet printheads


Fujifilm Dimatix QSRJM 256/10

� Silicon MEMS

technology

� 256 Nozzles,

single row

� 100dpi native

resolution

� Native drop

size 10pl


Confidential 6

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


Confidential 7

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.


Confidential 8

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

Deliverable 11.11

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


Confidential

rop visualisation system image s at printing frequencies from 1kHz to

ied voltage in most cases has trapezoid shape wit


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


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

9

s at printing frequencies from 1kHz to

trapezoid shape with pulse widths of


oth printheads channel acoustic was investigated in

plied voltage was optimised for reliable jetting.

Integration of multiple printheads into single pass system


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.


Confidential 10

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.


Confidential 11

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


Confidential 12

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


Confidential 13

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.


Confidential 14

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


Confidential 15

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.

deliverable 11.11 demonstration of single pass inkjet printing … · 2017-04-25 · avai lable but...

Documents