Inkjet Ink Printability. A Problem worth Solving. Patrick Smith.

Patrick Smith, Senior Lecturer at University of Sheffield

We have known Patrick for a number of years now. He has supported InPrint, presented at our events and demonstrated that he is an inkjet innovator by leading some key projects and developments with his work at University of Sheffield. In this interview, Marcus Timson talks asks him about his next challenge which is focused on a key issue for Inkjet - Ink printability.

What is ink printability Patrick? Please explain.

The next phase for inkjet we think will be helped by going back to the fundamentals to the printability of inkjet and also how the industry has moved onto water based inks and non-porous substrates and ink lifetime.

Ink lifetime is most important. The current academic definition of printability doesn’t deal with whether it will always print. Knowing that the ink will print and perform consistently in various places and with various heads and machines is an assumed quality characteristic. But it isn’t easy.

Printability is defined using a dimensional number, Z. But this number Z doesn’t take into account vapour pressure and temperature variations, which changes  viscosity. Right now, we don’t have an academic definition of how ink will perform over a lifetime. We can’t tell you if the ink will always continue printing.  This is some work we are trying to get started with Cambridge and Leeds (Universities). This is a research consortium we are forming and these three organisations are a natural fit.

So the three universities will work together on this?

Yes, we complement one another and are all committed to the development of Inkjet. Leeds knows ink chemistry very well. Cambridge have a good lab and equipment, Sheffield will provide the mathematician and I will coordinate.

Once we have achieved this we will share it with the industry. We don’t want to patent it. This is not the mission. We want to help the market improve and make it freely available and all the community can benefit from it. I am an academic and I want to demonstrate I can do this on an academic level in collaboration with other leading academics. I don’t see it as a business proposition really. Practically speaking it is about finding answers to difficult questions. Once we have it I hope people are able to use it and it will help the market develop for inkjet.

So to some extent, is it about standardisation?

Yes, but not entirely. There is an indicator of printability. The original definition was if your Z number was between 1-10 then it was considered to be OK. Today, this has changed a little and there are variations and you can get higher numbers to print and we are now finding lots of exceptions to this initial model. A key issue for a manufacturer is will my ink print and continue to print? And will my ink keep printing the same quality in different locations around the world? Our solution will provide more data and understanding - a lot of people will be interested in the answers by defining ink printability lifetime. It will be very useful.

So solving this could be a significant contribution?

Yes. If it is approximately €5,000 for an inkjet head and approximately €500-1000 for the inkthen as the ink is cheaper, sub-consciously people think it is the component more likely to fail. Print heads have a narrow range of printability and with the push to water-based inks printability continues to be an issue. We think our work can help. Ultimately, the more we can ensure ink printablity, the more we understand the dispensing devices.

It is very early days, we are forming the consortium and are confident that together with Leeds and Cambridge that we can make a good contribution.

Has inkjet, in your view, become a mature tech?

With digital print and digital packaging inkjet is established as a very promising tech to use. Clearly, it is growing and will be used in a promising market with excellent growth. Now printing onto new surfaces, new ink formulation, and there is more pressure to move away from volatile solvents to water based means. So if we solve this problem then it will be very helpful for the future of inkjet.

So what are the factors influencing print lifetime?

Having spoken to a number of ink manufacturers - being able to address this is a critical.

Water is a  challenging liquid to print. Viscosity is low, 1 centipoise, so a difficult so viscosity modifier is added.. If we use the term Z, then water at room temperature should give a Z value of 73, which means it should not print because the number is way too high. However, in the lab we can print water.

Water-based inks are more environmentally benign and have Health and Safety benefits too.

As we develop our consortium, we  would be interested in having industrial ink and inkjet head companies partner with us. We are keen to collaborate and this initiative has benefits for us all.

If you’re interested in finding out more or would like to support or get involved then contact Patrick directly on email: patrick.smith@sheffield.ac.uk