The challenges of high-speed inkjet printing in the offset world

There are increasing expectations to be able to the print the same paper by offset and inkjet printing either during the same printing time, hybrid printing, or to be printed with inkjet after offset printing. In hybrid printing, one-colour printing is quite often utilized to "personalize" the printed product. This certainly puts new challenges on the absorption properties of offset coating paper grades. From the offset printing point of view, the structure should not absorb the oil and resins of the ink too quickly into the paper structure and so raise the splitting forces in the printing nips. However, when considering the inkjet, the really high ink amount, compared to the amount of offset ink, should absorb very quickly into the structure. The absorption volume of coating layer should also be high for use with inkjet. However, in offset printing the pore volume does not need to be high. In both cases the colorant of the ink should stay in the top part of the coating layer. The aim of this work was to clarify how the structure of offset and inkjet coatings affects the print quality of high-speed inkjet printed surface. The results show that offset coatings have too low porosity and too large pore diameters to prevent the colorant of inkjet ink to penetrate too deep into the coating structure. The inkjet dye fixing requires the opposite charges between the ink colorant and the coating layer. It seems that the optimal coating layer structure for the multipurpose printing needs a compromise in the structural properties of nowadays offset and inkjet coatings.