Note: This article appeared in 2020. Custom solutions and conversions remain part of our service.
When printing flexible packaging substrates, digital printing repeatedly reaches its limits. Experienced users often find the solution. This article describes improved web guiding for HP Indigo 4000 series roll-fed presses that allows even stretchable substrates to be printed without problems.
PrintsPaul regularly holds practical digital printing workshops at its own training centre in Eschweiler and knows the requirements of the ws4000, 4050, 4500 and 4600 models in detail. Users want to know what their machine can do, which techniques can be integrated and which conversions are possible. Functional modifications can significantly extend the range of substrates.
Drawbacks of the standard equipment
As delivered from the factory, two vacuum boxes generate the web tension, one in the unwinder and one behind the print units. The web is always centred. The guides have to be set by hand and quite often damage the web edges. Uneven tension makes the web wander, leading to web breaks, downtime and waste. On top of that come high noise levels, high energy demand from the pumps and many lines across the shop floor.
Advantages of the new development
PrintsPaul replaces the vacuum boxes with two pneumatically controlled groups of dancer rollers, one in the unwind and one directly behind the print unit. The longer web path acts as a tension buffer. All web guiding components are centrally controlled, and jerky movements and web breaks no longer occur. The print image no longer has to be centred and can, for example, be offset to one side.
More materials
Thanks to the tension buffer, even materials that were considered unprintable with the factory equipment can run: very thin and stretchable films with thicknesses from 15 to 450 µm, such as BOPP, PE and PET mono films, PP/PE laminates, shrink sleeves and kitchen roll papers.
Conversion
Installing both dancer roller systems takes one working day. The units do not need their own power connections, and the original parts remain in the machine and can be reactivated. All 4000 series machines can be converted. PrintsPaul has already converted several machines, including an HP Indigo ws4050 at Thiekötter in Münster.
