Why press pre-setting is important
In this supporting article we explore why press pre-setting is important, and why press ink-key curve optimisation is essential.
The advantages of press pre-setting
Press pre-setting provides information to the press about the ink coverage of a job. How much ink is required for each colour, and importantly where on the sheet the ink is. The ‘area coverage information’ is translated by the press into ink-key openings, which set each ink-key position to allow more or less ink through into the ink roller chain, eventually making contact with the plate, offset blanket and finally the paper.
The ink film thickness/ink density is important and allowing just the right amount of ink into the ink roller chain at the job start will deliver the desired densities to the sheet most quickly. This translates into reduced make-ready times and reduced waste sheets, which in turns translate to reduced costs.
See our ‘makeready calculator’ for an indication of potential cost savings.
Once press pre-setting has been implemented it is essential the ‘ink-key pre-setting curves’ on the press (also known as characteristic curves) are calibrated to convert the area coverage supplied in the CIP3/PPF file into the appropriate ink-key opening.
The appropriate ‘conversion’ for each colour (from a number provided by the pre-setting file into a physical press ink-key opening) will be different depending on target densities, paper type, ink type etc. It is therefore essential this is optimised on each press.
The importance of pre-setting and optimisation cannot be over emphasised when it comes to on-press or near press colour measurement systems, such as Heidelberg’s InpressControl, ImageControl or AXISControl. These high-end colour measurement systems regulate ink film thickness very precisely and will highlight (and attempt to correct) any discrepancies between target and actual densities immediately.
The number of sheets required to meet the target depends very much on the ‘starting position’ and in the absence of optimised ink-key pre-setting these ink regulation systems will not perform well, resulting in extended makereadies, follow-ups, waste sheets and much frustration.
Note: Formerly with Heidelberg, Steve has 35 years’ experience in the print industry. As Heidelberg Print Colour Specialist Steve led Heidelberg UK’s PCM activities, specialising in press pre-setting, optimisation and colour calibration.