The audience of TheIJC 2019 could submit their questions to speakers via the conference app. Many presentations sparked multiple questions and not all of them could be answered during the session. We have therefore collected responses from several speakers and we publish them below.
“Particle sizing: An overview of myths and misconceptions about particle size” by Wolf-Dieter Wagner, Soliton
Is it possible to measure non-diluted ink samples?
With the Accusizer it is not possible to measure directly undiluted ink samples. As this is an extinction measurement above a particle concentration of 9,000 #/ml there is a higher probability of coincidence – means particles could come at the same time and place through the cell and are counted as one large particle. However, with the Accusizer AD we offer a system with autodilution. In this system, the customer injects an undiluted sample into a vessel and the system automatically dilutes down to 5,000-8,000 #/ml and then starts the measurement. This system is widely used to characterise inks for inkjet printers, especially for detecting a few oversized particles that can block the nozzle
“Infrared hybrid system for simultaneous multi-type drying” by Dr Larisa von Riewel, Heraeus
How do you measure the dryness of the print after different drying conditions?
1) Dynamical measurements with NIR Moisture Meter Model KJT-130, 2) Steady measurements with an offline standalone Moisture Analyzer by Mettler.
“Advanced resin technologies for inkjet packaging applications” by Paul Hönen, DSM
How good is the latency of the showed ink in case of using a printhead without throughflow?
The tests were done with a throughflow printhead (Fuji Samba). We have not tested the latency of the resin in a non-throughflow printhead. In the meantime, I can also confirm that the resin is used also in non-throughflow printheads with good latency results.
“Inkjet market update in graphics, packaging and industrial sectors” by Dr Sean Smyth, Smithers
Water based or UV ink: Which will be the major especially in book printing market in the future?
Overwhelmingly it is water based inks used in book printing, where the high-speed, single-pass press lines deliver complete, paginated book blocks and signatures in high volumes, as part of book manufacturing systems. Most of this volume is mono text sections, but increasingly there is full-colour text and inkjet sheetfed machines print some covers and jackets. There is limited UV, with some covers and books printed on the Konica Minolta AccurioJet KM-1 B2 format machine, for example.
“Tolerances in industrial inkjet printing of μ-electronic device components” by Kalyan Yoti Mitra, Fraunhofer ENAS
In order to make circuits, a reliability of 100% is needed. What is needed to increase reliability?
The main point to consider here is to use the correct industrial equipment, off-the-shelf materials, high stability / accuracy (non-batch wise processing) and to follow the route of lab to fab.
If you want to improve the printing parameters in electronics, should you use a more fine printhead to help your research?
This could be a possibility, but the interface of the printhead should be open for the researchers, that they can play with the waveforms and other vital process parameters. Additionally, the ink flow system (complex inks) inside the printhead system should also be simple and not complicated. Yes, then it can surely help.
“Understanding and optimising screeners” by Phil Collins, Global Inkjet Systems
You mentioned different colour impressions depending on if the droplets of e.g. yellow and magenta overlap or not. I would have thought this is only an issue with AM screens and not FM screens.
Colour and density shifts due to overlap happen in both AM and FM screens, because almost no real inks combine according to the perfect optical model, and in any area where there is a total of more than 100% of any two inks, there must be some overlap. However, my point on that slide was that whereas in AM the overlap is inevitable because of the fixed dot pattern, in FM there are implementation choices available which reduce overlap in the light to mid tones, hence preserving colour saturation. For example, consider an area of flat 50% Magenta and 50% Yellow, with an FM screen which produces a chequerboard pattern for each colour. This will produce the most marked shift possible depending on whether the colours overlap or interleave. The same overlap effect can be seen in AM by using all screens at the same angle, and in FM by using the same dither pattern for each colour, and in both cases it will produce muddy images. In AM the problem is managed by rotating the screens, and in FM by changing the dither patterns.
“New type of metallic pigment and the unique mechanism to achieve excellent specularity for inkjet printing” by Masashi Fujiwara, OIKE
Indium is very dense. Is settlement a problem in inkjet inks?
As time goes on, indium particles in dispersion settle. However, that is not aggregation and it is easy to disperse them again. We think that settlement is not major problem in inkjet inks.
What is the cost of indium vs. aluminium inkjet pigments bearing in mind that the raw material cost of indium is approx. 100 x the cost of aluminium?
Although the raw material cost of indium is 100 times of aluminium approximately, total manufacturing cost depend on occupation time of deposition and pulverizing process mainly. Assuming that we deposit materials on same area, the yield amount depends on the density of materials. Since density of indium is three times of aluminium approximately, deposition cost of aluminium becomes three times of indium approximately. Then, since deposited indium has island structure, it is easy to pulverize. On the other hand, to pulverize deposited aluminium, we need to pulverize it twice gradually at least. Thus we estimate that LeafPowder indium can be produced as same cost level as aluminium.
What about sedimentation of the pigment? Does it require a circulation system?
According to our experience of metallic ink printing test, we have printed aluminium and indium ink by SP-300V (Roland DG) without ink circulating system for a long while. However to avoid sedimentation of the pigment, we recommend a circulation system for better inkjet printing.
For what kind of ink types is this pigment suited? UV, solvent, water based?
As we showed several printed samples of indium at TheIJC 2019, printed UV ink sample show the highest circularity. However, since there is no metallic wate -based ink at this moment, we strongly expect indium to be used for it.
Is there a significant cost difference between Al and In particles to achieve a similar appearance? As I presented at TheIJC 2019, there is a different mechanism between aluminium and indium to achieve specularity. First, indium small particles are accumulated to "close-packed" structure, and then they contribute for concealing of printed layer and making flat surface. On the other hand, aluminium particles are over-rapped with almost same orientation, partially slanted. Even if we can make aluminium particle to be the same size as indium particle, we estimate not to get same specularity because of the difference between "shape" of aluminium and indium. Probably manufacturing cost of aluminium would be more than double of indium.
How are the aluminium and indium flakes passivated? Does the passivation have any effect on formulation into inks, for instance, for curing?
We are investigating surface modification method to passivate aluminium and indium against UV monomer. We find there are candidates of combination between monomers and passivation treatment by collaboration with chemical engineering company. We think there are solutions to passivate for curing in UV curable ink.
If Al particle size could be reduced, would it have similar speculation reflectance to In?
In order to achieve excellent specularity, I think there are two important points. First point is making "flat surface" and second one is "close-packed" structure in printed layer. Even if aluminium particle size could be reduced, it would not have similar specularity and reflection due to the shape and orientation of particles .
Can you please give your thoughts on the manufacturing/selling costs of indium based inkjet Inks and aluminium based inkjet inks?
Although the raw material cost of indium is 100 times of aluminium approximately, total manufacturing cost depend on occupation time of deposition and pulverizing process mainly. Based on our strategic thinking, we believe that indium can be accepted to inkjet inks instead of aluminium.
“Inkjet filtration application and Chinese inkjet market analysis” by Joyce Zhu, Cobetter Filtration
You mentioned bubbles as a potential problem. Is there an air impact already to the tight membrane filtration or only to the printhead itself?
Too many bubbles will impact the flow rate of tight membrane filtration, especially the hydrophilic membrane. If it is just dissolved gas, it only impacts the printhead and degasser will both solve these two problems.
What do you think are the best setups to filter water based pigment inks?
We recommend depth filter for the pre-filtering, removing the large particles and gel. But how to choose the right pore size, it depends on the particle distribution and particle count of the ink. In the last step, one can choose the membrane filter, with high filtration efficiency and no fibre releasing.
“Inkjet-capable resists for partial surface treatment of glass and metal” by Michael Groß, KIWO
Is a specific pre-treatment required for glass?
There is no need for pre-treatment. Resist or ink can be printed directly on glass surface.
“Ink and waveform performance optimisation” by Kyle Pucci, ImageXpert
What about rise and switch off times?
The rise and fall times of a waveform, sometimes referred to as slew rates, do have an impact on the drop formation and stability of the jetting as well. The impact of these values is a little bit more subtle than pulse width or voltage, and more difficult to standardise because the behaviour can vary more for each model of printhead. But in general, the faster the rise and fall times, the faster the ink will move and change directions inside the nozzle. This can have both positive and negative effects. The drops may eject at a slightly faster rate, but the nozzle is also refilling at a faster rate and might have increased risk of air ingestion.
Why do you start by finding a voltage before pulse width? Would you arrive at the same waveform if you were to begin with pulse width?
The recommended procedure is to first optimise the pulse width, then the voltage. The reason for this is that in general, the optimal pulse width is dependent on the ink formulation and printhead design (both of which are fixed in this instance) whereas the optimal voltage is also dependent on the pulse width. So it makes sense to first determine the pulse width, or at least get a rough idea of the starting point. From here, then you can tune the voltage as needed. In this particular presentation, voltage is mentioned first to illustrate the point that the pulse width optimization is best done on drops that form with as few satellites as possible. This can be achieved by turning down the voltage at the beginning to yield slower drops with better formation, before beginning the optimisation process.
“Overcoming challenges surrounding colour management in digital tile decoration through new approaches” by Jan Seguda, ColorGATE
Does the fingerprint technology require the printed sample to be the exact same image, or can it work on a "similar" image that has the same gamut?
It also works for images with similar colours. You can add multiple images to the fingerprint creation process (e.g. a design series), as well as add them later.
What is the colour accuracy of the measurement system compared to a spectrophotometer?
Comparison of two Rapid Spectro Cubes
maximum value = 4.49
average = 0.37
sigma = 0.37
weighted average = 0.27
10% patches <= 0.1
20% patches <= 0.2
30% patches <= 0.2
40% patches <= 0.2
50% patches <= 0.3
60% patches <= 0.3
70% patches <= 0.4
80% patches <= 0.5
90% patches <= 0.7
95% patches <= 1.0
100% patches <= 4.5
Comparison of RSC and xrite i1IO.
maximum value = 4.74
average = 0.42
sigma = 0.47
weighted average = 0.29
10% patches <= 0.1
20% patches <= 0.2
30% patches <= 0.2
40% patches <= 0.2
50% patches <= 0.3
60% patches <= 0.3
70% patches <= 0.4
80% patches <= 0.5
90% patches <= 0.8
95% patches <= 1.3
100% patches <= 4.7
“The JetFlow: Ink supply module for high-circulating printheads” by Dr Shahzad Khan, NTS Group
What is the temperature range?
It was designed for 32 degrees C. Many components are suitable for larger range. It needs to be investigated further for exact range.
The operational parameters appear suitable for aqueous inks. Has it been tested with UV?
UV ink has not been tested. It is expected to be an easy modification for the UV inks, still to be determined.
Which pressure accuracy can be achieved with this equipment?
Accuracy is +/- 5 mbar on the meniscus pressure.
“Robot guided functional inkjet printing on non-planar surfaces for electronic applications” by Robert Thalheim, Fraunhofer ENAS
Have you used distance sensors to keep the distance fixed between the printhead and the substrate?
There were no distance sensors involved within the experiments I have shown. The positioning was done by setting the path manually with a teach pendant.
Do you know why you have some blanks in the lines when printing upwards?
The blanks were due to clogged nozzles and not related to the upwards printing.
Why do you move printhead instead of substrate? How to control meniscus pressure ?
We are following both approaches in our experiments but I was only showing some insights of the ‘moving printhead’ technique. It is beneficial when it comes to accurate motion requirements on large area surfaces. The precision of an industrial robot is limited by the payload and when it comes to printing onto solid and heavy objects it is beneficial to move the printhead. The meniscus pressure was controlled by an external pump.
“Tips, tools and techniques for printhead waveform optimisation” by Matthew Pullen, Meteor Inkjet
How does the drop watching approach to waveform optimisation, overlap/compare with the complex rheology method from Trijet?
Complex rheology methods are complementary to drop watching techniques for evaluation and development of jettable fluids. Performing complex rheology evaluation gives insight into how an ink might behave in an inkjet actuator and its response to print frequency and waveform shapes using very small working volumes. A drop watcher will still be needed to refine the waveform performance based on the bulk ink response in the combined printing system of printhead, ink supply, fluid and waveform. Determining process windows, adjusting drop formation when building greyscale etc.
Please explain why a tickle pulse helps.
A tickle pulse or tickle waveform is an actuation or series of actuations that does not eject a droplet from the nozzle. The tickle pulse actuation moves ink in the channel and nozzle to reduce impact of either evaporation or rheology changes by keeping ink homogeneous and in a more steady shear state. Tickle pulses are beneficial even in printheads with at nozzle recirculation. Tickle pulses are highly effective in reducing latency effects in inks with either low open time (aqueous/solvent) or inks with large difference between static and dynamic surface tensions. Without a tickle pulse it is likely that artefacts in leading edge of print will be observed due to slow or failed ejections of first bytes of print data. Tickle pulses or tickle waveforms can be applied either on all white data if within the jetting waveform or by switching the driving mode (wfm) of the head between jobs or during pauses in production.
Would, not having the same PH electronics between the dropwatcher and the printer, cause differences in jetting performances?
In most cases no differences will be observable. In printheads where the analogue waveform is generated in the head driver card, subtle differences in pulse widths and amplitude outputs generated by the electronics may alter the jetting performance, so using a proven data path validated by the head manufacture is advised. Meteor support the largest number of printhead models so our commonality of hardware and software interface across these technologies gives the most flexibility to machine builders and fluids developers. Waveform files created on our system can easily be translated for use on other data paths.
“The novel silver nano ink: High conductive print without heating” by Tomohide Yoshida, Kao Corporation
Can inorganic material be encapsulated? For example, TiO2?
Yes, we could do it by similar encapsulation method.
Is the polymer coating around the silver particles removed by sintering?
Yes, we think so.
Are specific sintering condition required? Is a specific polymer material used to facilitate the sintering?
Yes, we design the polymer dispersant not only for stability but also for smooth sintering.
Where did the polymer go at room temperature? Have you done EDX/ToF-SIMS?
Not yet but I will do these analysis. Thank you.
Is there a difference in electro-conductivity of encapsulated silver particles compared to commercial silver particles?
It is hard to compare equivalent sintering conditions but as far as we know, there are no significance differences.
“How to attract and keep the best talent in inkjet” by Dorinda Gibbons, Profile Recruitment
How to choose the three top performers. Management or the workfloor?
I would suggest you look at who is most important to the success of the business, and consider are they happy and if not have open and frank conversations with them. Ultimately this is an exercise to get you thinking about the key players in your business and make sure they are engaged, happy and content and not looking to leave.
From your experience, is there something universities could be doing better to help graduates to be attractive for recruitment in the industry?
I would suggest work experience is always useful especially gap years where they can have a year or some experience in industry. I am always happy to speak to graduates to discuss their plans for the future and help them into industry.
“New developments in print quality characterisation: How topography analysis provides additional insights in combination with ink-substrate interaction studies” by Sebastian Schaubach, Dataphysics
How long does a 3D scan take for a given area?
It very much depends on the used objective and the height differences of the measured area. An area of 2 mm on 2 mm can be measured in 5 seconds.
“Another challenge of Kyocera with a new printhead design platform” by Shin Ishikura, Kyocera
What is the cooling temperature requirement?
22 – 25 degree C at 0.6 – 0.9 L/min for the efficient cooling.
Is the IJP 1.0 being discontinued and if so, is there a conversion header to allow new 600 dpi head to be used in the old systems without new electronics?
We have no plan to stop conventional models at this moment.
Is IJP 2.0 jetting viscosity same as 1.0?
What is the ink viscosity range requirement?
For Aq models 6.0 +/- 0.5 mPa*s at 32 degree C ideally.
Are there also printheads on base of new recirculating IJP 2.0 technology with bigger drop sizes than 2.8 pl for higher particle loads?
We are considering some models with recirculation over 2.8 pl models.
Is the nozzle adjustment method by the waveform not sensitive for a crosstalk?
The nozzle adjustment cannot be specific reason to worsen crosstalk effect although it requires confirmation through printing test.
Is the head heated ?
Yes. It is equipped with a heater and temperature control circuit.
“Fully inkjet-printed, air stable OLEDs for signage and packaging applications” by Patrick Barkowski, Inuru
What is the performance (brightness etc.) of the OLED? How is the cathode realised?
Brightness goes over few thousands cd/m^2, we use between 500 to 1k cd/m^2. Printed cathode is one of our core IP.
Are you using commercial materials to print your OLEDs or are you synthesising them yourselves? If so, can you say something about the material class?
Most materials we do synthesise ourselves, some we do in cooperation with partners. The material class is confidential but I am happy to discuss more via direct contact.
“Flow induced damage and chemistry within printing flow systems” by Dr Niamh Fox, University of Cambridge
Have you looked at copolymers and using the breakage regime, potentially to generate functionality at the point of jetting? Can the results of this work help with the design of polymers that are more robust?
We hope that the understanding gained in this work aids the design of more robust polymers.
Could the limit of minimum molecular weight achieved with ethyl acetate/hexanbe based on the single pass nature?
This is true to some extent, the cleavage is affected by the single pass nature of the flow experiments. However, in general the limiting molecular weight is more strongly governed by the polymer-solvent interaction, both how good a solvent is for the polymer in question and also how well the solvent transduced mechanical energy to the polymer.
Is there something known about the mechanism when a polymer backbone is cleaved when it is stretched? Is the cleavage homolytic, generating a biradical?
This is exactly correct, the cleavage is homolytic creating two radical-terminated polymer strands.
“Optimum drying for inkjet processes” by Dr Kai K.O. Bär, Adphos
Is it possible to remove water and glycol from primer treated film such as easily shrink over 60℃?
If there is time or the right boundary conditions, e.g. with reduced pressure conditions, water as well as glycol(s) could be removed at low elevated ambient temperatures. But for fast processes like printing and esp. inkjet printing applications (say ≥ 30 m/min) with adphosNIR drying technology, we have successfully removed water even as low as 35-40 °C. Glycols with boiling temperatures > 200-300 °C, have such a low partial pressure at this temperature, that a removal by evaporation cannot be reached. But depending on the boundary conditions, with extreme high NIR-energy density processing, as we can realise with the adphos propriety technology, with the generated milliseconds possible water vapor cloud, we can remove partially adjacent fixed glycol molecules (by disruption) and reduce/remove so at least a fraction of the glycol. That is enough for the given application at a temperature processed before the substrate starts shrinking, must be investigated and evaluated in detail for the specific application case. We offer to do so.
If you evaporate one ton of ink per hour, how do you handle that half ton of glycols contained in the vapor? It is certainly not allowed to emit that into the environment.
Depending on the specific application, ink recipe and process configuration, the moisture/exhaust treatment has to be managed. The specific exhaust treatment is finalised in conjunction with the line manufacturer and line owner.
Does NIR heat all colours and ink types at the same rate?
Inks, assuming graphical application inks, which focus on their specific colours mainly, have to show in the visible light spectrum a different absorption, to allow the colour distinguishing. Depending on how the colours are achieved, dyes, pigments, organic or inorganic, there is/can be a different absorption characteristic pronounced, even same colour for same application can have different absorption characteristics outside in the visible light spectrum (of 380-780 nm) like in the UV (< 380 nm) or (IR) λ (> 780 nm). Typical pigmented inks for analogue as well as IJ printing applications show a spectral absorption behaviour. So, only black (as a graphite based pigment) shows wide wavelength range absorption. All the other shown colours: C, M, Y have a fall down absorption in or close to the visible wavelength spectrum. Above 900 nm, no absorption is given for none of these coloured pigments. Since the NIR light sources show a non-monochrome emission spectrum, the fraction of energy spectrum in the visible light and adjacent near infrared wavelength range (< 1,500 nm) are allowing only the direct absorption of heat in these pigments. Otherwise, like in the larger wave IR (short, mid and long wave IR) the fraction < 1,500 nm is minor (second order) and therefore no absorption at all results from the printed colour pattern there. The heat absorption and then the drying of the wet printed coloured pattern is only a result after heating the substrate and have heat conduction into the coloured pattern. With NIR-based energy sources a direct heating of the given colour pigment is achieved. No other drying process is possible by drying the printed pattern, without the necessity of heating the complete substrate. So since the absorption is slightly different for the different influencing colours for the NIR-heating devices, the required drying energy for the different coloured printing pattern is therefore also not equal. Even though this is given, it can be managed to dry completely full coloured printed pattern properly today for all non-coated as well as coated substrates, even for low temperature resistant, non-absorbing plastic film substrates, water based coloured inks applications with adphosNIR-drying solutions.
Did you investigate the drying of inks on paper only or also on unabsorbant substrates?
adphos provides advancedNIR (aNIR) drying solutions for a large variety of printing/coating applications in a wide range of substrates: porous and partially porous substrates (paper, wooden based, ceramics, natural textiles, food), as well as non-absorbing (coated papers, plastic films, glass, ceramics, metals, concrete, polymer based textiles) substrates.
“Promoting curing speed: Ideal surfactants for LED curing inkjet inks” by Dr Vedran Durasevic, Evonik
I did not get the point with the adhesion on PP and PE. How did you solve this problem?
What we aimed to convey in the talk was that wetting and adhesion are sometimes interpreted as the same. While both contribute to the overall functionality and appearance of the print, i.e. the print quality, substrate wetting is a pre-requisite for good adhesion. Although, all tested rigid plates, regardless of their chemical composition could easily be wetted out, adhesion was impossible on PP and PE in which case we failed to functionalise the substrate with the sufficient amount of ‘oxygen containing’ groups that enable adhesion. Measured Surface Free Energy Values favoured the hypothesis. Combining excellent wettability with maintaining over-printability is another challenge well known in the printing industry. Siloxane based additives are here used to lower the surface tension of printing fluids designed for printing onto polyolefin substrates. These not only act as wetting additives, however, contribute to adhesion by increasing the smoothness of the surface, which arises from the silicone presence on the surface of the film. That silicone presence could prove challenging in the deposition of subsequent printing fluids. The recently launched additive TEGO® GLIDE 496 combines excellent compatibility, reduction of surface tension and maintains high surface energy of the ink film, thus providing an ink receptive layer.
How do you expect a metallic substrate to stack up compared to the plastics your efforts focused on?
In comparison, adhesion to metallic substrates is easier to achieve than to challenging ‘plastic’ substrates of low qualities, inherently low surface energies and delivered with impurities to the market.
To improve adhesion on metallic substrates, the use of unsaturated polyester based co-binders from the TEGO® ADDBOND range is recommended. The selection and the inclusion levels of the right co-binder will depend on the technology of the developed ink.