DI presses have not taken a significant share of the sheetfed press market. High-cost equipment and consumables have made the presses difficult for offset companies to justify. The market shares this view. After 15 years, fewer than 2,000 have been installed worldwide. Putting multiple CTP heads on-press is expensive and raises concerns about lost press time if an imaging system fails. Most conventional technology is aimed at improving turnaround, with automatic plateloading. Presetting one platesetter offers similar benefits of quick makeready for multiple presses. This situation would change if on-press imaging could reuse the plates for new jobs.
Re-imageable plates change the economics and could take on-press imaging to the next stage, with cleaning and imaging part of a controlled makeready process. The first re-imageable offset printing system was MAN Roland's DICOweb, which uses cylinder sleeves imaged and erased for each job. The imaging system is costly and MAN has not adopted it for sheetfed presses. Mitsubishi's reusable plate system (RPS) offers repeated erasing and reimaging in an offline version using a aluminium sleeve coated with a polymer film. After printing, the film is washed and a new coating applied. Sleeves can be used for 20 cycles and have a life of 100,000 impressions.
Choice of technologies
Three competing technologies are being explored as the basis of re-imageable technology:
Ferroelectric ceramics involves anelectric charge changing the magnetism in the material. Ink-accepting dots are created by electromagnetic attraction, in the same way as a copier with a permanent save feature at offset speeds.
Thermic materials repel ink or dampening solution when warmed.
Switchable polymers involve altering the physicochemical properties of polymers with light energy from oleophilic to oleophobic, then cleaning, wiping and re-exposing.
Kodak's Creo uses plateless digital offset printing (DOP) technology, which involves a reusable substrate that is cleaned off the previous image, sprayed with a lithographic coating, laser imaged and printed normally. The press cylinder drum can be sprayed directly, but press designers will favour replaceable substrates, as the risk of scratching is high otherwise. The design target is for a weekly change, with animaging speed of four minutes for B1. While first demonstrated in 2000,commercial reality is still unclear, particularly under Kodak'sownership, as a leading single-use plate supplier.
Agfa has Litespeed, a no-process coating that is sprayed on to the plate or cylinder surface and imaged with a thermal laser source. Processing is completed when non-image areas are removed by the inking system on press.
For printers, such technology promises significant advantages. The offset industry would benefit from the reduced costs and makeready times afforded by re-imageable plates. Imaging a B1 press would take less than a minute. The cleaning/coating/drying cycle would be performed by adapting the blanket and cylinder wash systems. The overall turnaround target would be less than five minutes using JDF set-up data.
A major plus is the ability for new suppliers to retro-fit equipment on to existing sheetfed and web presses, which gives the huge base of offset presses a further lease of life. A retro-fit implemented on a modern 8-10 unit sheetfed press could reduce makereadies by 75%. Five-minute set-ups allow more jobs to be printed, which is increasingly important with the continuing decline in run lengths.
In a few years, DI technology will either disappear into a technology cul de sac or be a significant addition to automated computer-integrated manufacture, with plates reused in situ.
Sean Smyth is an independent "techie" providing support for organisations looking to applytechnology effectively. Smyth can be contacted on sean_smyth@dsl.pipex.com
30-second briefing on: Imaging technology
On-press imaging systems have been a niche technology since their launch in 1991. They have not fulfilled their promise, due to their limited formats and lack of flexibility of colours. Heidelberg's decision not to offer DI systems could herald the death-knell for the technology. But there is potential light at the end of the tunnel, using re-imageable plates.
Reimaging is used on-press by the MAN DICOweb and off-press by Mitsubishi's RPS system. Creo and Agfa have unveiled technology that is not yet commercially available.
The impact of the technology could provide a significant boost to the competitive position of offset, as it could be retro-fitted to existing presses to significantly improve their productivity.
There is much scepticism about the likely success of re-imageable plates, particularly from coated-plate manufacturers. The chances of success will be determined by plate suppliers' strategy. Success is more likely as they are owned by suppliers of imaging equipment. The use of plates would drop, but the cost would be significantly higher to provide benefits for user and supplier.
For more information, speak to suppliers of CTP and plates at Ipex.
