Details:
Summary:
Pressure on reducing prices and a market demand for customisation and shorter production runs give cause for investigating alternatives to conventional printing. Traditional technologies, such as flexography and offset, are all using static printing forms, while a digital printing unit prints information directly from the data file. Hence, the latter alternative makes it possible to produce short runs, even providing every printed copy with a specific design. However, one disadvantage, when high volumes are produced, is the higher cost per copy for digital printing. Another approach is to use hybrid printing, where digital printing is used to add information onto substrates, pre-printed using conventional printing technology. Conventional technology can then be used to gain large-scale advantages, while digital printing makes it is possible to customise certain parts of the original design for any printed copy, if desired. Hence, information can be tailored to fit different segments or specific customer needs It is always important to achieve a high and constant print quality. When a digital print is added onto a pre-printed substrate, it is essential that the final result from this combination is of high print quality too. Hence, it is important to know how the different technologies interact and how this can be measured. The aim of this investigation was to identify factors that influence the print quality of hybrid printed matter and that are important to consider in the design and evaluation of a hybrid printing production. The focus in this study was on hybrid printed matter, where the added print was supposed to blend in with the pre-printed background. Samples had been made by carrying out flexography and inkjet printing trials, together with a hybrid printing trial. In the latter trial, printed objects were added by a high-speed inkjet press to a pre-printed flexography substrate. The objects added consisted of elements for technical measurements and pictorial elements, aimed at fitting into a flexography pre-printed image background, for visual evaluations. The hybrid printed pictorial samples had different characteristics. The added print and the background had a similar or different colour content. The added print was put onto a pre-printed or an unprinted area and it was applied so that it bordered directly on or indirectly on the pre-printed elements in the background. All the trials were done on uncoated paper. Furthermore, the parameters of the added print, e.g. print speed and colour intensity, were varied. Technical measurements, assumed to be significant for print quality, such as colour density, print gloss, print mottle and sharpness, were obtained from both printing techniques, separately and from combinations of them, with areas where inkjet had been printed on top of the pre-printed flexography backgrounds. Moreover, visual assessments were done by a panel to determine the visual impression of hybrid printed samples. The study resulted in a quality model, identifying important factors to consider when preparing for a hybrid printing production and when evaluating print quality. The model clearly demonstrates the strong influence of the characteristics of hybrid print. These characteristics will affect the way a hybrid printing production should be planned and carried out.