Novel device for determining the effect of jetting shear on the stability of inkjet ink

Inkjet printing is a rapidly expanding technology for non-contact digital printing. The focus for the technology has changed from office printing of text and image documents increasingly toward wider applications, including large-scale printing of on demand books and packaging or ultra-small-scale functional printing of microscopic volumes of precious/rare materials formulated for use in precisely printed digitally defined patterning arrays, such as printed diagnostics, flexible electronics, anti-counterfeiting, etc. For efficiency, as well as resource management and conservation, predicting the stable runnability of an inkjet ink remains largely a key unknown. Today the only way to know often means simply trialling it, which at best takes time, and at worst incurs costs rectifying possible equipment damage. We propose a mechanically driven displacement device providing constant high-shear flow rate through an extended capillary. This differs from a standard capillary viscometer, which is commonly pressure driven only and lacks the ability to mimic consistent volume flow inkjetting. The novel method is used to study the aqueous colloidal stability of polymer solution, latex polymer suspensions and complete pigment-containing inks, including a reference pigment only comprising suspension. The results reveal the tendency to build agglomerates, determined by dynamic light scattering particle size distribution, optical and electron microscopy. Liquid phase parameters, including surface tension, and suspension intrinsic viscosity are also studied. Repeated application of high shear is seen to act as a milling process for pigment and agglomerate building tendency for latex binder. Consequences for ink jettability are discussed.