Theory of Ink Transfer in HP-Indigo Digital Press Machines

摘要

In the digital press machines developed and manufactured by HP Indigo Division the world leader in the field, the ink is transferred from roller to roller and finally from roller to the substrate. A fundamental demand to digital printing is that each page can be different from the previous one. This requires 100% transfer efficiency, i.e. no ink should be left behind. In the previous NIP conference a model for the electrically driven transfer from the photoconductor roller to the intermediate transfer member roller (ITM drum) was presented . This year we treat the transfer from the ITM drum to the substrate. Rather than providing an exact model, the aim here has been delivering a simple theory that is capable of pointing out general trends and the main parameters leading to perfect transfer. It will be shown that only ink possessing elastic properties can lead to 100% transfer. Based on this, the ink sandwiched between the ITM drum and the substrate is approximated as real elastic solid having rough surface. The model leads to the conclusions that the main factors governing transfer efficiency are the elastic modulus of the ink and the surfaces of the ITM drum and the substrate. The ink will adhere to that surface where the composite modulus of the surface and the ink is substantially larger. Other parameters influencing transfer are surface energy and roughness. Since elastic modulus varies from material to material by several orders of magnitude and strongly depends on temperature while the range of surface energy and roughness is much more limited, it is natural to control ink transfer through properly selecting the surface modulus of the ITM drum and the temperature dependence of the modulus of the ink. Finally, it will be shown that HP Indigo's unique Electrolnk and ITM drum ideally fulfill the requirements pinpointed by the theory and ensure 100% ink transfer to the substrate.