The Hague Display card, is a collaboration between the Munich University of Applied Sciences and the California Polytechnic State University. It is a special card using an electrochrome and thermochromic display. These displays are the best to comply, especially when they are driven by external power sources, as a battery or an USB micro cable.
The design of the card is an old man who rides a balloon and looks through his telescope at night.
The Transatlantic Project Team from the Cal Poly State University and the Munich University of Applied Science have developed and produced 2000 hand-out demonstrators for the IDTechEx Printed Electronics Conferences in Santa Clara and Berlin, and worked as a successful team.
Divided in small groups, each specialised at one topic in the process, we learned to work as a unit. And with the great guidance of our team leader, Christian Jakob, we had a very exciting and successful experience to complete this project together.
The project work was performed within the mandatory modules ‘Project I’ and ‘Project II’ of the program ‘Print and Media Technology’ and advised by Prof. Dr. Ulrich Moosheimer. The project demonstrates how successful task based learning can be.
Electrochromic display (HM)
By connecting a USB micro plug to the transparent front page, the electrochromic display is activated and the balloon as well as the telescope changes to a blue colour.
An electrochromic display consists of an electrolyte layer, an electrochromic polymer, a substrate and a protective coating. The polymer changes its colour under electric potential in a chemical reaction. An electrical potential forces Li+ ions to move from the electrolyte to the PEDOT layer. There it changes the conjugated double bonds of the PEDOT and the PEDOT changes it colour to blue.
- Cylinder Die Cutting for USB:
The substrate for the electrochromic display is PET foil. The card will change the colour with the usual micro USB cable for mobile phones to get enough electricity. This means that the current flow has to be transferred onto the printed conducting paths. Before printing, the foil is die-cut by the rotary cutting machine in the form of the USB plug. The foil is charged with corona pretreatment for an improved wetting of the PEDOT. Another advantage of die-cutting first is that register marks can be stamped out on the foil as well, this is to have an exact justification in the printing process.
- Printing PEDOT:
The PEDOT conducting paths and the contact points of the USB are printed on the inside of the foil by a screen printer. The PEDOT is our electrochromic polymer for the display. After printing, the PEDOT becomes almost transparent and fluent and has to dry in the oven. After being dried at 70°C for 10 minutes, the PEDOT turns to solid, smear-proof and scratch resistant.
- Printing Lithium:
Lithium is our layer for the electrochromic display to change the colour of the PEDOT into blue. But Lithium by itself is unable to print, so carrier-material is necessary. A special developed lithium ink is printed on the foil because it has a good printing result, is easy to regulate and has an efficient electrochromic display. But the lithium ions have to be fluent to guarantee the function of the display. Therefore we have to minimize the loss of moisture. This condition is achieved by the lamination.
The foil for the lamination is a self-adhesive foil, has to fit precisely and without bubbles and is our protective coating for the electrochromic display. It looks water clear and without side effects. After printing, the dried display passes the electrostatic charge. Close to the ionizing rod dust is blown off by compressed air. The adhesive foil is cut in the correct size and afterwards glued instantly on the printed display.
We focused on aligning the conducting paths between the two parts and paid attention to a high transparency of the printed electronic parts in connection with a high opacity of the switched on blue display areas. We also combined the design and the functionality of the PEDOT conducting paths.
Thermochromic Display (Cal Poly)
Cal Poly developed the design “The Hague” and added thermochromics inks. By applying a battery to the card, heating elements increase the temperature at selected spots, the thermochromic inks gets transparent and stars appear in the sky. The thermochromics ink will reactivate by touch for a period of time after being activated.
The cardboard is printed with an electrophotographic printer on the front and the back and afterwards the silver conducting paths are printed on the cardboard by the screen printer.
The conducting paths on the cardboard and the conducting paths on the foil are connected over pads in the binding to enable current flow between the two. It had to be taken care that the electricity flows only at the intended contact points as soon as the foil and the cardboard are combined. In the end, the foil and the cardboard are sewed together.
Before placing the Cal Poly card into the Munich Brochure the stars are activated by a 9 V battery block and the Munich Brochure is plugged to a USB mirco power supply. The stars appear and the moon shows up. Inside the brochure the Cal Poly card closes a switch and the moon appears. Now the man in the blue stripped balloon sees the stars and the moon through his blue coloured telescope.
Due to the high volume and the production possibilities, the demonstrator shall fulfill the following demands:
- Printed electronics as key feature
- Disposable in domestic waste
- Stand-alone demonstrator of each university
- Additional feature by combining the demonstrator of both universities
- Attractive design
- Easy to produce on standard printing machines of both universities
- Low material costs
- High reliability
- Easy to handle
The Hague Display was not only a successful student project; it is also interesting from an economic point of view: The costs for a print run of 4000 pieces are estimated to be around 30ct per piece.
The following video shows the production process for our printed display.
This project was created in Print and Media Technology at the University of Applied Sciences in Munich in a team of 15 students during the summer semester of 2015.
Both universities thank their sponsors for their great support of the project: