Flexo printing technology is more advanced than ever before. With faster presses, new image carriers, and better inks, flexo printing is perhaps the most efficient printing process out there.
But, that doesn’t mean printers aren’t still haunted by flexo printing defects. Even the most efficient pressroom can run into issues, regardless of their care and maintenance practices or fingerprinting tests.
Understanding common flexo printing defects such as ghosting is crucial to avoid downtime and improve pressroom efficiency.
What Is Ghosting in Flexo Printing?
Ghosting is the faint image produced during flexo printing that you can see on large, solid areas. It's mostly a result of the anilox failing to consistently or completely recover adequate ink densities, also known as a failure to properly rewet the cells.
It can also happen when the anilox and the print calendar aren't similar, leading to a shadow image in several spots. Most ghosting problems are more apparent in darker colors like blue, green, brown, and red.
Causes of Ghosting in Flexo Printing
You’ll most likely experience ghosting if you have problems with the porosity of the anilox cells’ depth and the walls, which affect ink transfer to the substrate. With increased press speeds, it lowers the ability to fill the anilox cells with ink. It also hampers the possibility of continuously delivering a consistent ink film thickness to the plates. When there’s a poor ink transfer, ghosting can occur.
Still, if the viscosity is too high, the ink cannot flow back into the cells and fill the cells completely. This means it can pick up ink from the chamber or the fountain roll, but fail to release it from the cells. This leads to ghosting.
Other causes of ghosting:
- Mechanical issues
- Your anilox roll isn’t clean
- Ink starvation
- Chambered doctor blade not adapted
How Can You Bust That Ghost?
When trying to eliminate ghosting in flexo printing, your primary aim should be to improve the anilox cells' ability to function efficiently when filling and transferring ink. If you experience ghosting in flexo printing, you can try out the following diagnostic solutions:
- Identify the colors where ghosting occurs and replace the anilox roll with another of a similar cell volume, but of a coarser screen. It will deliver an equal amount of ink to the plate, but with reduced ink starvation as long as the transfer rate is compatible.
- Decrease or increase the machine's speed, depending on the effect you’re seeing.
- If you have a higher-viscosity ink (i.e. water-based ink), replace it. Slow inks lead to drying on the anilox rolls.
- Try using a higher volume of the anilox roller.
- Use a specific design of the chambered doctor blade to ensure that ink floods the cells.
- Increase the ink level or try adding pressure on the chambered doctor blade.
- Add a solvent to increase the ink's fluidity to flood the cells while also avoiding ink starvation.
- Lower the pressure on the blade to reduce the heat and friction at the ink's sheer point.
- If possible,run trouble inks on the decks with enclosed systems or add the dwell times between blades. It will help rewet the anilox roll.
- Put the ghost color on the black deck to ensure you use the entire chamber for wetting.
Who Ya Gonna Call?
While your flexo printing ghost isn’t a giant marshmallow man (unless it is -- then you have another issue), it’s still a pesky problem. Taking the necessary steps to mitigate ghosting in your flexo printing operations can reduce waste and improve your print speeds.
To learn more about all types of printing defects, check out our printing defects guide!