Use of Analytical Techniques to Characterize the Stability of Difficult Ink Jet Pigmented Systems

Abstract

Pigmented inks are now commonplace in all types of ink jet systems, from industrial to desktop. To achieve robust printer performance in the printheads an understanding of the ink's stability is vital even before testing in a printhead is undertaken. It also provides valuable information regarding settling and shelf life. All of this analytical work highlights the requirement for the correct formulation before printer trials can begin.Several new analytical techniques are available for determining the stability of pigment dispersions. One of these is sedimentometry using the Turbiscan system. This system involves the scanning of a column of ink using a near infrared monochromatic pulsed LED. The system detects transmitted light through the sample and also backscattered light from particulate material in the ink. The system takes a scan every 40 microns through the sample and multiple scans can be overlaid to give information about stability with time.Using this system several difficult pigment types have been successfully incorporated into ink jet inks. These include various heavy inorganic pigments of particle sizes up to 2 microns. Metallic powders with particle size distributions in the order of D 50 of 2.0 to 3.5 microns and D 90 of 4.5 to 6.5 have been successfully stabilised and subsequently printed. This level of particle size is unheard of in the desktop market where inks are commonly filtered to below 0.5 microns and often 0.2 microns.Use of these analytical techniques has highlighted issues such as chemical and physical instability long before conventional techniques and can then allow for the correct choice of dispersants, resins and solvents to be chosen produce a stable ink system that can then be reliably printed through ink jet printers.