Common offset printing issues and how to reduce them
Even small irregularities in the printing process can slow down production and lower quality. Therefore, it helps to know typical offset printing problems and how to limit them. Below we describe three frequent issues: set-off of fresh ink, ink rub-off, and ink repelling.
1. Set-off of fresh ink (ink transferring in the stack)
Set-off happens when fresh ink transfers onto the next sheets in the pile. In other words, lower sheets “give” ink to the sheets above them. Moreover, several factors can cause this effect, so it is worth identifying the real source and choosing the right action.
- Too much ink on low-absorbency paper – use standard ink feed, add a suitable additive, and also apply powder spray and adjust sheet piling.
- Pile too high at delivery – the weight removes the air cushion between sheets; therefore, print to a lower pile and use powder spray.
- Incorrect delivery settings (often with heavy boards) – reduce the drop height and set the gripper opening timing. In addition, the sheet should fall tightly into the pile.
- Poor sheet flatness – choose higher-quality paper without wavy edges.
- Electrostatic charge on sheets – use smaller, looser piles because this helps maintain print quality.
As you can see, set-off may come from different causes, however you can limit it with the right setup and workflow. For more practical tips on offset printing issues, see the other articles on our blog.
2. Ink rub-off
During production, issues can appear that reduce the visual quality of the print. Therefore, it is useful to know how to react to common defects. One of them is ink rub-off. Below are key causes and methods that can reduce this effect.
Over-diluted ink
Ink can rub off when the ink is too diluted. Then the binder soaks into the substrate too quickly, so the pigment does not bond properly on the surface. A practical solution is to bind pigments by overprinting with binder or by using an oil-based printing varnish.
Poorly sized (over-absorbent) paper
Another cause is paper with incorrect sizing and excessive absorbency. Then ink penetrates too strongly and the pigment does not bond with the binder, therefore quality drops. Such stock should be overprinted with an oil-based printing varnish. However, because oxidative drying inks react differently, the underprint can slow absorption. If the run is already completed, binder overprinting, printing paste, or a high-gloss oil-based varnish can help.
Too little binder
Rub-off can also occur when the ink contains too little binder. Then you can add binder to the ink or apply a binder overprint. As a result, the print looks better and readability improves.
3. Ink repelling
Many factors can reduce print quality and legibility, yet ink repelling is one of the typical issues. Fortunately, you can limit this defect and avoid an unattractive result.
Causes and ways to reduce it
Ink repelling appears when the first layer dries too much and forms a surface that is too hard to accept the next layer. Most often, this happens due to excessive drier or an overly long gap between the first and second colour. Therefore, choose the method based on the run size.
- Small runs – gently wipe the print surface with cotton.
- Large runs – overprint with printing varnish and print the next colour while the varnish is still drying.
- Alternative – reduce or eliminate the use of drier when possible.
When you reduce ink repelling, the print looks clean and visually strong. However, correct diagnosis matters, because then you can apply the right method for both small and large runs.
Need help with print quality? Write to us and describe the issue—our team will suggest practical next steps.