The experience of an automatic reel change on a 4.2 metre wide gravure press never ceases to amaze. Likewise flying reel changes have been standard on newspaper and commercial web offset presses for more than a generation.
Nobody can afford to stop the press to make a hand splice before printing can begin again. But in high speed inkjet printing this is commonplace.
This will surely change as inkjet moves from transactional and book printing into commercial print spaces. With a manual operation to replace a spent reel with a new one taking ten minutes every hour the imperative must be to keep the press running wherever possible.
As presses become wider the number of impressions lost during this time increases and the weight of each reel increases making automation almost essential.
Hunkeler has stated that it has no interest in automatic reel handling and it is the dominant force currently in paper handling for continuous feed digital presses. Others have, however, perceived a gap. Tecnau, from a similar background as Hunkeler, has developed an automatic reel changing system, while from the litho arena, Goss Contiweb and B&W Megtec have developed reel stands that are designed for use with inkjet presses.
The biggest challenge that has been a barrier is the height of the splice. Conventionally the start of one reel is overlaid on the end of the previous reel using adhesive tape. This has worked well with existing technology, but it increases the calliper of the paper and the risk of striking and damaging some very expensive printheads.
With manual changing there is time to withdraw the print heads to both protect them and clean the nozzle plate. With automatic changing some mechanical means of raising the heads, or more realistically lowering the web path is needed.
While there is going to be an advantage to automating the reel change, there is no need to employ the technology that has been developed to do this at the speed of gravure and web offset presses. Inkjet does not operate at these speeds.
The Tecnau U40 splicer has two reel positions, one running and one loaded with the next reel. The paper is turned through 90º and vertically into a central tower where the splice action takes place.
At this point a signal is sent to the press to ensure that splice and printhead do not meet and then to ensure that the white paper around the splice area is removed before it can become part of the final product.
Tecnau has designed the unit to cope with mixing paper types and quality and web width between rolls to support book on demand production. Maximum web width however is 521mm, paper range from 50-180gsm and operating speed at 150m/minute.
Megtec has supplied reel handling to printers using HP T400 series machines, including that at Mengis Druck in Switzerland. It was installed to handle newspaper for daily production of 22,000 newspapers. This, however, has ceased because additional web offset capacity became available at the right price and time slots. The equipment remains in place to cope with increasing demand for book and commercial printing.
The variability that an inkjet press will need to cope with has spurred Contiweb to develop a solution that can switch between media types on the fly as different jobs arrive. It has installed the technology on the T490 at Rotomail in Milan which has provided a great deal of feedback into running different styles of paper at speeds up to 300m/min.
“It took a little getting used to in terms of the applications and paper qualities, running from 80gsm to 250gsm as standard. The range of papers we have to tackle is much wider than we would expect in offset litho printing,” says Bert Schoonderbeek, managing director of Contiweb.
It can also switch from 76cm to 100cm reels as the sequence of jobs requires to provide the flexibility that digital printing demands, particularly where the press is handling short run jobs, down to 200-300 metres of paper. “This is completely different to offset where web printing is about running the same job for long periods,” he says. “That makes it a little more challenging to build.”
But the flexibility of the technology enables the print company to plan jobs more freely rather than having to batch jobs according to the paper they need as well as allowing the user to run the press continuously – at least as far as paper handling is concerned.
The other key advantage comes with paper savings. Where the printer has to stop the press for a new reel or for a different paper, there will be many metres of unusable paper passing through the press as it accelerates to its running speed.
While printing relatively long run jobs, this is probably acceptable, but as these machines enter the commercial print market where each job wants a different paper, this could become wasteful as well as relatively expensive.
Contiweb can also supply a rewind unit able to accommodate multiple reels as it has at Rotomail. The real gain from the technology comes when rewinding is replaced by inline operation. Just as with the reel handling, this means a different approach. “In offset printing everything is a fixed length, in digital everything needs to be variable,” he says. It is another complication to consider.
The Hunkeler UW6 is suited to most continuous feed digital print applications, but with the drive towards applications in direct mail, magazine and catalogue printing, automated web handling is starting to become necessary.