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Troubleshooting guide for inline waterbase coating.

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  • 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.


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