Troubleshooting guide for inline waterbase coating.

Click on the problem to view the solution.

• Uneven coating weights on sheet

  PROBLEM

  Uneven coating weights on sheet

  CAUSE

  • Uneven pressure between coater rollers.
  • Uneven pressure between applicator roller and blanket.
  • Uneven pressure between blanket and impression.
  • Dried coating within coating system.
  • Applicator roll to blanket ratio unbalanced

  SOLUTION

  • Adjust coater rollers. KISS CONTACT
  • Adjust applicator roller to blanket KISS CONTACT
  • Adjust pressures and/or check for low areas, smashes in blanket and packing.
  • Clean rollers, blanket and impressing cylinder.
  • Synchronize applicator roll to press speed.

• Build-up of coating on blanket, outside of sheet.

  PROBLEM

  Build-up of coating on blanket, outside of sheet.

  CAUSE

  • Blanket packing not trimmed properly.
  • Not enough packing behind blanket.
  • Too much pressure between applicator roller and blanket.

  SOLUTION

  • Cut packing at least _ inch smaller than sheet size on all sides.
  • Add .006 to .008 more packing.
  • Adjust applicator roller away from blanket. KISS CONTACT

• Sheet Curl

  PROBLEM

  Sheet Curl

  CAUSE

  • Stock absorbs too much water.
  • Excessive heat.
  • Mechanical distortion.
  • Incorrect coating.

  SOLUTION

  • Precondition Stock.
  • Check moisture content of paper.
  • Stock moisture content should be at 5-6%. Too low moisture content (<5%) leads to excessive distortion as water is absorbed from the coating.
  • Use paper stocks of 80 lb. or higher.
  • Lessen the coating weight via metering or lowering the viscosity.
  • Reduce heat.
  • Run the coating to edge of the sheet if possible.
  • Use inks with a lower water pickup. Check the sheet guides, most notably star wheels can distort the sheet.
  • Engage sheet decurler if available.
  • Contact your C&A representative

• Bead of coating on side edges of the sheet.

  PROBLEM

  Bead of coating on side edges of the sheet.

  CAUSE

  • Too much pressure between applicator roller and blanket.
  • Coating volume too high.

  SOLUTION

  • Adjust applicator roller away from blanket. KISS CONTACT
  • Reduce application volume.

• Build-up of coating on trailing edge of the blanket.

  PROBLEM

  Build-up of coating on trailing edge of the blanket.

  CAUSE

  • Too much pressure between applicator roller and blanket.
  • Blanket packing not trimmed properly.
  • Too much pressure between blanket and impression cylinder.
  • Applicator roller speed faster than blanket surface speed.
  • Dirty blanket.

  SOLUTION

  • Adjust blanket from impression. KISS CONTACT
  • Packing at least _ inch shorter than sheet length.
  • Applicator roller and blanket surface speeds should be the same.
  • Clean blankets thoroughly.

• Spitting or slinging

  PROBLEM

  Spitting or slinging

  CAUSE

  • Coating accumulating on edge of rollers.
  • Flaring on end of rubber roller.
  • Coating foaming.
  • Coating drying too fast.
  • Level in reservoir pan too high.

  SOLUTION

  • Reduce viscosity.
  • Reduce the amount applied.
  • Adjust roller speeds.
  • Apply grease to outside ends of applicator roller.
  • Clean end of rollers, or change roller.
  • Contact your C&A representative.

• Foaming

  PROBLEM

  Foaming

  CAUSE

  • Level in reservoir pan too low.
  • Air being introduced into circulating system.
  • Coating pump pumping too fast.
  • Air entrapment in coating.
  • Viscosity too low.
  • Contamination of coating.

  SOLUTION

  • Increase coating level in coating pan.
  • Check pump seals and piping for air leaks.
  • Reduce coating pump speed.
  • Eliminate any free fall of liquid in your re-circulating system
  • Change to fresh drum of coating.
  • Avoid extended idling time.
  • Thoroughly flush lines prior to use.

• Mud-cracking or Crazing

  PROBLEM

  Mud-cracking or Crazing

  CAUSE

  • Coating dries faster than ink. Ink shrinkage causes breakup of coating film.
  • Low relative humidity.
  • Incompatibility of ink and coating.

  SOLUTION

  • Check water pickup of ink.
  • Increase coating weight.
  • Increase IR, reduce air knives.
  • Climate control the pressroom.
  • Alternative coating might be needed.
  • Contact your C&A representative.

• Backtrapping or ink buildup on blanket. Sometimes appears as voids in the coating film.

  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

• Drying – The coating will not dry within acceptable limits, even though "nothing" has changed from last run.

  PROBLEM

  Drying – The coating will not dry within acceptable limits, even though “nothing” has changed from last run.

  CAUSE

  • Dryer failure.
  • The system was likely near its limit without the operator being aware of this threshold.
  • Excessive coat weight.
  • Coating viscosity is too high.
  • High relative humidity.
  • Heavy ink coverage.
  • Excessive moisture content in the stock.
  • Variations in stock absorbency.

  SOLUTION

  • Check IR lamps, air movement & exhaust.
  • A faster drying coating might be needed.
  • Other adjustments would be:
    1. Boost heat
    2. Increase air flow
    3. Slow the press down
    4. Lower the coat weight
    5. Check the ink density
  • Lower coat weight
    1. With coater settings.
    2. By decreasing viscosity.
  • In the summertime, ambient air has a higher moisture content and therefore less ability to dry. If the pressroom is not climate controlled, boost the heat and airflow or try a faster drying coating.
  • This can be a problem especially with dark colors. A more efficient drying system or coating might be needed. The ink water pick up should also be investigated as this can sometimes be a swing factor. Run stronger ink of possible.
  • Try changing the paper stock first. If the drying problem does not persist with the new stock, check the original stock for moisture content. The ideal range is 5-6%. Higher than that can severely limit absorption, thus adversely affecting drying speed.

• Rings or ridges of coating on rollers or blankets.

  PROBLEM

  Rings or ridges of coating on rollers or blankets.

  CAUSE

  • Not enough pressure between rollers or blanket.
  • Not enough coating being applied.
  • Too much coating being applied.

  SOLUTION

  • Adjust rollers and blanket settings, tighten NIP.
  • Increase coating viscosity.
  • Check for low areas in roll blanket and blanket packing. Replace or repack if necessary.
  • Reduce coating viscosity.

• "Orange Peel" Surface appearance.

  PROBLEM

  “Orange Peel” Surface appearance.

  CAUSE

  • Too much coating applied to the blanket.
  • Coating viscosity too high (too thick).

  SOLUTION

  • Reduce roller speeds to apply less coating.
  • Reduce coating viscosity (make thinner).
  • Check NIP pressure.

• "Cratering", "Crawling" or "Pinholing".

  PROBLEM

  “Cratering”, “Crawling” or “Pinholing”.

  CAUSE

  • Coating not rewetting, or trapping over the wet ink because of waxes in inks.
  • Too much reducer or additive in the inks.

  SOLUTION

  • Use NO WAX INKS.
  • Consult CAC about materials with better wetting properties.
  • Eliminate or change additives for inks.

• "Volcanoing" or "Rupturing" of coating surface.

  PROBLEM

  “Volcanoing” or “Rupturing” of coating surface.

  CAUSE

  • Volatiles in ink film burst through coating resulting in voids.

  SOLUTION

  • Use lower VOC inks.
  • Lower pile or dryer temperature.

• Poor UV adhesion (flaking, crawling or scratching).

  PROBLEM

  Poor UV adhesion (flaking, crawling or scratching).

  CAUSE

  • Proper primer not used.
  • Waxes in inks.
  • Water entrapment.
  • Trapped ink oils or solvents.
  • UV crawling (not wetting properly).

  SOLUTION

  • Use qualified primer coating only.
  • Use wax free inks.
  • Use glycol-free etch.
  • Allow additional drying time prior to UV coating.
  • Use low VOC or high solid inks.
  • Avoid excessive use of open-time, spray or additives.
  • Consult UV supplier for wetting agent, flow aid, or different UV coating formulation.

• Gas Ghosting

  PROBLEM

  Gas Ghosting

  CAUSE

  • Waxes in inks.
  • Retardation of ink oxidation by stock.
  • Too much solvents in inks.
  • Selected stock is prone to ghosting.
  • Turning a job too quickly.

  SOLUTION

  • Reduce waxes.
  • Change to more porous stock.
  • Second pass through the drying system.
  • Reduce solvents in ink.
  • Run heavy solids side first.
  • Change stock.
  • Allow as long as possible before printing second side.

• Offset, Blocking or Picking of Non Porous Stocks

  PROBLEM

  Offset, Blocking or Picking of Non Porous Stocks

  CAUSE

  • Inadequate drying.
  • Inks remain soft.
  • Excessive pile height.
  • High heat.
  • Too much coating applied.
  • High Humidity.
  • Defective spray powder unit.

  SOLUTION

  • Use maximum air knives and extraction.
  • Only use enough heat to set and dry the inks.
  • Maintain ink/water balance.
  • Use specially formulated inks for non-porous stocks.
  • Run smaller lifts.
  • Reduce Viscosity.
  • Slow coater down, increase NIP pressure.
  • Maintain pressroom climate control.
  • Inspect and clean spray unit and run minimal amounts.

• Loss of Ink Density

  PROBLEM

  Loss of Ink Density

  CAUSE

  • De-wetting of ink.

  SOLUTION

  • Use faster drying coating.
  • Monitor ink/water balance.
  • Avoid glycols and glycol ethers in fountain solution.
  • Run stronger inks allowing for thinner film thickness.
  • Use faster setting inks.
  • Change to a more porous stock.
  • If possible, leave open unit between coating and ink station.