Sunday, 27 May 2012

Talk : Prof Hutchings on Inkjet Printing

A fascinating public lecture was held recently by the The University of Nottingham and the Institute of Materials. Presented by Professor Ian Hutchings from the University of Cambridge, the talk was entitled “From Gutenberg to the Digital Age: the Challenges and Opportunities of Inkjet Printing”

Professor Ian Hutchings is the GKN Professor of Manufacturing Engineering. He is also a fellow of St John's College, Chairman of St John's Innovation Centre Ltd. and Editor-in-Chief of the international journal, Wear.

Prof Hutchings kicked off by outlining the differences between “conventional” and “inkjet” printing:

Conventional Printing
Uses a durable plate
Contact process
Good for making lots of identical copies

Flexible, can make a different image every time
Non nontact process
Any liquid can be printed, in principle

The Prof then outlined the history of inkjet technology, describing the main arcs of its development from its uptake in industiral labelling processes in the 1980s; to popular use in home and office printers in the 1990s; to current developments in printing on demand.

There are basically two types of inkjet printing:

Continuous Inkjet printing - where a few nozzles continuously eject ink drops, which are steered to make the required pattern (or are steered to some kind of ink recovery reservoir if not required to hit the print surface, such as for spaces etc)

Drop on Demand Inkjet printing - where a larger number of nozzles are used and each drop is individually addressed . This is the kind of print process we see in our domestic printers.

Prof Hutchings went on to delve into the detail of how the drops of ink are formed by explaining that there were two main processes. In the “thermal” process, some of the ink in the nozzle is heated so that it boils to form a bubble - which forces the rest of the ink out of the nozzle. In contrast, the “Piezo electric” process causes the wall of the nozzle to deform and push out the ink. The graphic below illustrates how they work.

Piezo electric vs thermal inkjet technology -
seems to be a dead heat in this case

The drop does not come out as a neat sphere but as a head with a long tail, as shown in the schematic below (which is based on data and images from this Cambridge Inkjet Research Centre)

Inkjets are called Inkjets for a reason. . .

As an aside, the Prof mentioned that the first continuous inkjet printer was the Kelvin Siphon recorder, developed in 1858 to automatically record telegraph signals.
Kelvin's Siphon recorder worked well,
but it would be awhile before he could print out pictures from I Can Has Cheezburger

Continuing to look at the nitty-gritty of the technology behind inkjet printing, Prof Hutchings explained that the ink drop undergoes tremendous changes in the shear forces and acceleration during its transition from nozzle to paper, and the ink formulation has to be sufficiently robust to accommodate this, as well as being able to last for several years before use.

The talk then moved on talk about examples of industrial inkjet printing, including the XAAR1000 printhead (that has has 1000 nozzles and the ability to cover 130m2 per hr) and the Kodak Prosper 5000KL state-of-the-art digital book printing system

Incidentally, the XAAR website has links to some incredible state-of-the-art printing videos on YouTube. The ones on the Atlantic Zeiser GAMMA 70 printer , the Cretaprinter Real Printer printing onto ceramic tiles, and the Presta Label printing system particularly caught NSB's attention.

In terms of full printing machinery, the Kodak Prosper 5000KL is a digital book printing system of fearsome power, able to run at 200metres per minute whilst printing up to 600mm wide.

Thus far, the talk had stayed on relatively familiar territory by discussing only how to print inks onto paper substrates. But now Prof Hutchings took things to a different level by discussing how one could print metals, pointing out that there were a number of ways to do this, including the following :

i) Print molten metal.
ii) Print a suspension of metal particles in a liquid (e.g. water) and sinter.
iii) Print a metal containing compound and react to leave only metal.

This part of the talk is admirably covered by one of Prof Hutchings powerpoint presentations that is available online . Some of the images in the presentation are very impressive and show where the technology might be heading.

Prof Hutchings pointed out that inkjet drops were always 10microns or bigger, so whilst it was possible to make larger electronic structures such as solder dot arrays, it was unlikely that it would be possible to print down to the 10s of nm level that is typical for modern semiconductors.

However, inkjet printing was at the ideal scale for technologies such as displays and was a key enabling technology allowing the commercial manufacture of PLED technology screens.

But the possibilities of ink-jet printing do not end with metals. The 3D manufacturing / rapid prototyping revolution that is currently underway (in which physical components are made by printing them layer by layer) means that polymer parts with constantly increasing service temperature capabilities can be made. Similar advances are being made with printing of 3D tissue and vascular systems.

In both of these cases, it is the ability of inkjet printing to make a single, tailored and unique component that is key to their success. You can get an overview of what this technology can do, at least from the industrial components and prototyping viewpoint in this video

You can read more about organ printing in this presentation by Vladimir Mironov, one of the pioneers in this field (see also this New Scientist article).

Images : Animated GIF, Kelvin Syphon

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