Comets or Streak Lines:

Possible Causes:

Solution:

  • Comet/streak line changes with the oscillation of the doctor blade
  •  Check for foreign particles under the doctor blade.
  • Clean the doctor blade.

 

  • Comet/streak line does not change position 
  •  Check the cylinder for any damage.
  • Lightly polish or replace the cylinder.

 

  • Random streak lines
  • Check the substrate for dust pick up during the press run.
  • Filter the ink for foreign particles/unground pigments

 

 

Blocking:

Possible Causes:

Solution:

  • Ink is drying too slow
  •  Use faster drying solvents 
  • Decrease the printing speed
  • Increase air flow and temperature of blower
  •  Rewind pressure is too high
  •  Decrease the rewind pressure
  •  Over plasticized inks
  •  Contact ink supplier.
  • Add anti-blocking compound.
  • Film is treated on both sides
  • Use one side treated film; or
  • Use anti-blocking compound.

 

  

Hickeys: 

Possible Causes:

Solution:

  • Dust or foreign particles in the substrate
  • Check and clean the substrate 
  • Change the substrate.
  •  Foreign particles on the Impression cylinder
  •  Check and clean the impression cylinder

   

 

Mottle:    

Possible Causes:

Solution:

  • Ink viscosity is too low
  • Add fresh ink to increase the viscosity
  • Increase machine speed
  • Too much pressure on impression cylinder
  • Adjust impression cylinder pressure

 

   

 

Drying in:

Possible Causes:

Solution:

  • Ink viscosity is too high
  • Adjust ink viscosity
  • Decrease printing speed.
  • Ink is drying too fast
  • Add slow drying solvents
  • Increase printing speed.
  • Hot air coming to the nip
  • Reduce blower pressure
  • Minimize the hot air going to the nip.

 

 

Adhesion:

Possible Causes:

Solution:

  • Poor treatment of substrate
  •  Treat substrate to appropriate treatment level
  • Improper ink for the substrate
  • Contact ink supplier and request for the right ink for the substrate.