This article is part of the FLEXO FLAW FIXING series
What is Ghosting Effect?
Ghosting is to describe the faint picture formed and is particularly noticeable in extensive solid regions. Ghosting effect in flexo happens mainly due to the anilox failing to consistently or completely recover acceptable ink densities, also known as failing to rewet the cells adequately.
It can also occur when the anilox and the print calendar are not identical, resulting in a shadow picture in multiple places. Most ghosting issues are more noticeable in darker hues such as blue, green, brown, and red.
Flaws of Ghosting effect
If you have issues with the porosity of the anilox cells, their depth, and walls, which impact ink transfer to the substrate, you will most likely have ghosting. Increased press speeds reduce the ability to fill anilox cells with ink. It also makes it challenging to continually produce a constant ink layer thickness to the plates. Ghosting can occur when ink transfer is inadequate.
However, if the viscosity is too great, the ink cannot flow back into the cells and fill them. This cause implies that it can take ink from the chamber or the fountain roll but not release it from the cells. Other reasons for ghosting include:
- Mechanical problems;
- Your anilox roll is filthy;
- Ink deficiency;
- The chambered doctor blade is not suitable;
What are the Causes of Flexo Printing Ghosting?
Following are the causes of the ghosting effect in flexography.
- Mechanical Problems
Mechanical ghosts are frequently apparent as soon as the press sheet enters the press’s delivery area. They are the following:
- Light Print Ghost
- A “light print ghost” appears as a light or dark picture of another area of the press form in huge solid or dark halftones. The arrangement of the press sheet elements and the constraints of the press-inking technology is to blame.
- This defect can happen when graphic components on the press touch the form rollers immediately before huge regions of high solid ink coverage. Before the rollers contact the stable, the visual elements lose more ink from the form roller than the press can make up for within time.
- As a result, the solid receives less ink in specific locations, and the graphic components are reliable as a light picture.
- Dark Print Ghost
- A “dark print ghost” develops when knocked out graphic components immediately precede a region of intense ink coverage.
- A light print ghost is the inverse of this. The knockout, in this case, can cause extra ink to linger on rollers in the reversal, resulting in a dark picture of the design appearing in the vast solid.
- The same tactics used to avoid light print ghosts are used to prevent dark print ghosts.
- Plate Ghost/Blanket Ghost
- A “plate ghost” or “blanket ghost” occurs when graphic components enter the printing as latent pictures.
- This issue typically happens on multicolor presses when the press form on one of the color units sensitizes the plate of the following color unit.
- Proper desensitization of the afflicted plate and ink modifications should resolve the issue; nevertheless, replacing the plate and blanket may need in some cases.
- Filthy Anilox Roll
Check the cleanliness and physical condition of the anilox roller as part of regular maintenance and clean or replace it as necessary. Anilox cells frequently become clogged with dried ink or other pollutants, reducing the amount the anilox can transport.
- Ink Deficiency
All successful flexographic printing relies on ink transfer. The amount of ink is transferred through the printing process’s components and eventually onto the substrate. The deficiency of ink is the leading cause of the ghosting effect in flexography.
- Incompatible Chambered Doctor Blade
Change the chambered doctor blade that is not suitable for flexo printing cause the ghosting effect.
Solutions To Prevent Ghosting Effect In Flexo Printing
When attempting to reduce ghosting in flexo printing, your primary goal should be to increase the anilox cells’ capacity to fill and transfer ink effectively. If you have ghosting issues with flexo printing, you can attempt the following diagnostic solutions:
- Identify the colors that ghost and replace the anilox roll with one with a similar cell volume but a coarser screen. As long as the transfer rate is compatible, it will send an equal amount of ink to the plate with less ink famine.
- Depending on the effect you observe, reduce or raise the machine’s speed.
- Replace it with a more excellent viscosity ink (water-based ink). Slow inks cause anilox rolls to dry out.
- Increase the volume of the anilox roller.
- To ensure that ink floods the cells, use a particular design of a chambered doctor blade.
- Increase the ink level or experiment with applying pressure on the chambered doctor blade.
- To flood the cells while avoiding ink famine, add a solvent to improve the fluidity of the ink.
- Decrease the pressure on the blade to reduce heat and friction at the sheer point of the ink.
- Run problem inks on decks with enclosed systems if feasible, or add dwell periods between blades. It will aid in rewetting the anilox roll.
- Put the ghost colour on the black deck to guarantee that you soak the whole chamber.