Ink-jet Printing of Materials for Light-Emitting Displays: the Stability of Printed Liquid Lines

Wednesday, January 10, 2001 - 10:15am - 11:00am
Keller 3-180
Paul Duineveld (Philips Research Laboratory)
Philips is investigating displays of light-emitting polymers. One of the advanta ges of polymers is that they can be applied from a solution which enables wet chemical processes as spin coating. This technique is suitable for making monochrome displays. However, for full colour displays this is not useful because these pol ymers can not withstand ething solutions. Therefore selective patterning techniques ha ve to be applied. Ink-jet printing is an interesting technique because it can generate high resolution patterns and is suitable for mass production. First a brief overview is given of the display principles, the drop formation (e specially the high molecular weight polymer solutions give special drop formation) and som e examples of ink-jet printed displays. The main part of the talk will be devoted to an instability of a printed line. I t is well known from the literature that a liquid ridge is unstable. Two boundary conditio ns for instabilities have been studied recently. These are: constant contact angle and constant contact line, e.g. when printing a hot wax on a cold substrate. The printed polymers have interesting properties. Depending on the conditions o f the substrate the wetting of the polymer solutions can be changed. This includes bot h the advancing and the receding contact angles. Under several conditions the receding contct angle is zero. This can result in a peculiar instability of a printed li ne, that depends on several variables. In this presentation experiments and a first theor etical model to describe this instability will be presented.