Printing Innovation Asia Issue 8 2021
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Label Printing and the Rollers in your printing press There are many types of rollers in your printing press and they all have unique functions and uses. Let’s take you through the various roller types, what they do, the coating of the roller surface, shore hardness and other functions.
Path rollers The most common and widely used roller is the path roller. It’s responsible for transporting the substrate through the press. It’s important to keep these rollers unsoiled with regular cleaning and free of any dents or scratches. If you dent or scratch your path roller it can lead to scratches and dents in your web requiring replacement. There’s a coating on all path rollers to help sustain their long life required. It’s advised not to use sandpaper, steel wool or even a Scotch-Brite pad or similar abrasive pad as they will remove the coating. Using box cutter knives (used daily as a printer) is a definite no when removing dried ink or even from a wrap around on a web break as they will scratch and ruin your roller. Even when there’s pressure to get the job running, it’s worth a few extra minutes to save your roller.
A good way to clean metal rollers is by using acetate and water to safely remove ink and paper dust, especially if you’re using a paper-backed self-adhesive substrate. A weekly schedule should be made for cleaning rollers and the press. For the impression roller, regular maintenance will help eliminate any issues with marking or poor printing. Teflon coated path rollers are usually only used in the turner bar part of the press and sometimes swapped in and out when needed. These rollers have a non-stick coating for when you do de-lam/re-lam work and now have the adhesive side of the substrate touching the path rollers. If you do not use a Teflon coated roller you will get wrap around and will be unable to run with a regular path roller. I’ve seen printers use the backing of the plate mounting tape; this can also create issues, so it’s best to have sufficient Teflon coated rollers available. Nip rollers Usually there are two nip rollers with adjustable pressure - some machines have three. They’re located at the unwind after the edge guide, and on the last print station towards the rewinder after the die and matrix stripping unit. Nip rollers can also be added to the lamination/cold foil unit and turner bar for re-lam/de-lam work, which provides the substrate and backing
film or paper to re-join. These provide tension in the press by a driven, infeed roller and rubber roller along with the braking system and load cells on more modern presses. As they’re made from rubber, it’s important not to cut on these rollers and damage them. For older machines that don’t automatically release the pressure during press shut down, make sure to lift them before you shut down or flat spots can occur causing instability and tension problems. Impression rollers The impression roller has the substrate that passes over the impression roller/ cylinder and the printing plate is set to this to transfer the image onto the substrate. This happens on all print stations. A driven impression roller can act as a nip roller if the printing plate has too much pressure. An MPS press has a free-running impression roller
