PROBLEM
Backtrapping or ink buildup on blanket. Sometimes appears as voids in the coating film.
CAUSE
  • Coater activating late, allowing ink to transfer to coating blanket at start-up.
  • Excessive pressure between blanket roll and impression roll causing squeeze out of coating and pick up of ink on blanket
  • Insufficient amount of coating being carried by blanket.
  • Ink volume too great for single station application or to allow sufficient bodying before coating application.
  • Ink tack too low, producing a weak strength ink film.
  • Excessive water pick up from fountain solution by ink causing extended open time and ink film weakness.
  • Coating not rewetting properly.
  • Blanket too soft or tacky due to having been washed repeatedly with petroleum solvent.
  • Improper blanket cleaning or possible contamination.
SOLUTION
  • Adjust coater ON/OFF timing switch.
  • Adjust roll contact to kiss pressure. Back off pressure until coating continuity lost and adjust to continuous film across sheet.
  • Adjust roll speed or coating viscosity to carry a thicker film of coating.
  • Where possible, apply the ink in 2 hits and/or move further back in rotation on press. Check density and adjust downward where indicated.
  • Increase tack of problem ink.
  • Check fountain solution balance, adjust pH as necessary.
  • Coating representative may suggest change of coating for this application. Additional rewetting agent may be required in coating.
  • Thorough removal of all cleaning solutions and other residue.
  • Apply blanket hardener or replace with a harder blanket.
  • Rinse or rewet blanket with water or water loving solution
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