Hazing (gravure print)
Hazing describes a visible ink mist in non-printing areas and leads to an increased colour density in printing areas. Hazing is one of the most common problems in garvure print and can have various causes.
Solutions to hazing:
- A too high ink viscosity leads too high stagnation pressure, which lifts the doctor blade bevel. Check viscosity and reduce if adding solvents or additives.
- Check ink on additives, such as binders.
- Check roughness values of impression cylinders within the chrome or copper. Cylinders, which are too smooth lead to a lower lubrication between doctor blade and impression cyclinder and causes friction. Re-polish or renew impression cylinders, if the problems continue.
- Check counterbalanced impression cylinders, if necessary balance.
- Check doctor blade reatainers for contamination or corrugated doctor blades. Clean doctor blade retainer and renew the supporting doctor blades, if necessary.
- Inspect the doctor blade's provision and use a harder setup or thicker supporting doctor blades.
- If hazing appears onesided, watch out for a correct parallelism of the doctor blades' bar to the impression cylinder.
- Check the doctor blade pressure, because excessive doctor blade pressure can sag the dotor blades' fibre and stagnation pressure elevates the colour of the fibre. Only use as little pressure as you can.
- Examine the doctor blades' angle for a too shallow setup. It can lead to an elevation of the fibre caused by stagnation pressure of the colour.
- Check the doctor blades' oscillation for an even motion without stopping. Oscillation should be between 10 and 30 mm.
- Check the doctor blades' stroke between doctor blade bevel and nip. If the doctor blades' stroke is too short, the excess ink on non-engraved areas will not allow sufficient time to dry.
- If the doctor blades' stroke can not be increased, use blast air at the squeegee stroke. Be careful when drying in vignettes.