ElectroInk is a dispersion of micron and submicron size polymer particles containing nanometer size colorant pigments in non-polar fluid. ElectroInk is in the core technology of digital printing press machines developed and manufactured by HP Indigo Division the world leader in the field of digital press machines. ElectroInk is a complex fluid exhibiting non-linear rheological properties. During the print process electrical field is applied to the ink that causes the ink particles to move in the field. Also, as the ink propagates from the container to the final substrate (paper) to be printed on, the concentration continuously increases; the ink is subjected to changes in temperature, pressure, shear, and electrical field; all transforming the rheological properties. As the concentration increases the ink ceases behaving as simple dispersion of non-interacting particles. Instead, the ink is better described as an interwoven structure of two continuous phases one being an elasto-viscous solid like substance made of from strongly interacting particles and dissolved liquid the other being the pure solvent.This model reminding a wet sponge is called the two-continuous phases model of ElectroInk. The movement of individual particles is replaced by the deformation of the solid like part described by the tools of mechanics and electrodynamics of continuous media. This model adequately describes the transfer process of the ink from roller to roller in the press under electrical field and predicts the relevant parameters leading to 100% transfer which is necessary to meet the principal requirement to digital printing vis. that each printed page can be different.In this presentation a short introduction to Indigo's special technology will be given followed by some general findings on the unique rheological and electrical properties of ElectroInk, and the two-continuous phases model will be introduced and applied to electrically assisted ink transfer process.Experimental data showing good agreement with the model will also be presented.
Peter Forgacs, Albert Teishev, "Electro-Rheological Model of HP-Indigo ElectroInk" in Proc. IS&T Int'l Conf. on Digital Printing Technologies and Digital Fabrication (NIP28), 2012, pp 348 - 351, https://doi.org/10.2352/ISSN.2169-4451.2012.28.1.art00021_2