KomaFoam

Fabrication: Laminating Troubleshooting

  • WARP!
    • Largest single issue in the process
  • Not bonding
  • "Puckering"
  • "Bubbles" or "Tunneling"


Warp

This is a big issue, but there are only a few root causes

  • Imbalanced tension
  • Imbalanced adhesive application (moisture)
  • No back mount, or different paper type
  • Excessive time between front and back mounts
  • Excessive adhesive

Guideline - if the foamboard is flat at the time it is converted, it is most likely one of the above process problems leading to the warp.


Tension induced Warp

tension induced warp

Results in MACHINE DIRECTION warp

Best to reduce tension to acceptable levels

Can be overcome by "weighting" the finished stack until it is back mounted

  • Although under tension, the glue completely cures in a flat state
  • This will not work for extreme cases
  • Most converters use this practice on ALL sheets


Imbalanced Adhesive / Moisture

imbalanced adhesive moisture

  • Moisture causes paper fibers to swell
  • With excess adhesive / moisture on one side, it will grow relative to the other
  • Typically this is cross-machine direction warp
  • Best if grain direction of print and board are opposite


No Back Mount

no back mounting

Ideal for the converter to back-mount to maintain flatness.

  • Both sides treated with adhesive (moisture)
  • Both sides under tension
  • Both sides have the same moisture transmission properties

Backmount is usually lighter paper to reduce costs, which is fine.

Without a backmount, the adhesive and print on one side will have a tendency to create potential for warp.

Different Paper Types

different paper types

Occasionally, a user will mount a photographic film, etc as the art work.

  • Prevents moisture transmission
  • As mount hangs and goes through humidity changes, the print side has slower responses
  • Results in warp that recovers ("bowing")

Ideal to mount the back with the same material, but better solution is to upgrade the substrate to a PVC product.


Timing between Front and Back Mounts

  • On machines that mount one side at a time, it is possible for the first mount to induce bow
    • With no "weighting" of the work in process, it is possible for the bow to "set" and become permanent
  • Ideal timing from front to back is about 24 hours to allow adhesive to cure, but moisture is still present
  • Storing in stacks best as moisture equilibrates from sheet to sheet in the stack.


Timing

timing

  • In a stack of fresh board, the moisture content will "equilibrate" from the mounted side of one sheet to the unmounted side of another
  • Best to keep the top sheet covered with plastic, and weighted if possible to keep it from bowing


Dry Environment

dry

  • In a dry environment, the top sheet will tend to throw off moisture, shrink on the top and bow upward at the edges
  • The opposite is true in a humid environment


Excess Adhesive

Using too much adhesive, or low solids content (less than 50% solids) can cause permanent warp

  • Rather than temporarily causing the paper to grow, it moves past a hysteresis point
  • Like a book dropped into a pool
    • It will dry, but the pages remain bloated

Excess adhesive costs MONEY, so there are good reasons to use as little as necessary


Excess Adhesive

excessive adhesive

  • Remarkably few converters measure adhesive usage accurately
  • Low effort, and high return in terms of material costs and quality
    • Minimum adhesive usage ensures minimum warp, puckering, bubbles, tunnels, etc.
  • Weigh a board before and after going through the coater
  • Take the difference in weight = adhesive application rate
  • Adjust coater gaps to get to target
  • A target will vary based on substrate, etc, but 3#/MSF wet is reasonable


Adhesive Types

Two main types - resin and dextrin

Resin

  • SBR, PVA, EVA based adhesives
  • High solids, excellent green strength, low usage requirements, but more expensive

Dextrin

  • Starch based
  • Typically lower solids, lower green strength, but less expensive

Dextrin is the adhesive of choice, but in the event that the lamination is particularly tricky (high gloss papers, coarse papers, etc) resin should be used.


Not Bonding

  • Rare issue
  • Typically too much or too little adhesive
  • Myriad of equipment problems
  • Rarely if ever the foamboard
    • Paper is ideal for bonding
    • Not possible to contaminate the surface without it being obvious
    • Paper is not made in the same mill as silicon coated grades etc.


Puckers and Tunnels

  • Typical defect from too much adhesive.
  • Excess moisture causes the print to swell to the point of lifting from the foamboard
  • Can be local puckers or create tunnels if the adhesive application is uneven
  • Cutting the print and inspecting under is telling - amount of adhesive should be obvious.


Bubbles

Caused by local delamination due to insufficient glue

  • Board depressions
  • Roll coater problems
    • Damaged rolls
    • Improperly gapped coater rolls
    • Improperly gapped laminator rolls

bubbles

Roll Gaps

roll gaps

  • Coating and Laminating rolls should be 0.010" (10 mils) less than board gauge (see figure above)
  • Ensures full contact in the coater
  • Ensures good pressure in the laminator


A Few Added Points on Lamination

KomaFoam is ideal for mounting jobs

  • Superior surface to corrugated - graphics "pop" better
  • Superior warp resistance due to clay coated liners (papers are partially sealed)
  • Superior converting characteristics
    • Good "rebound" in coaters and laminators
    • More even glue application
    • Better adhesive "hold-out" than corrugated

 

The information below provides further direction for fabricating KomaFoam. Click on the fabrication category for detailed instructions.